Mineralogy

MINERALOGY

NATURAL objects which are homogeneous in their mass, and in which no parts formed for special purposes can be distinguished, are termed “minerals”; and the branch of natural science which treats of these is termed mineralogy. Minerals differ from the structures treated of in botany and zoology in the three following particulars. (1) They differ in the mode of their formation; this has been accomplished, not by assimilation of matter, producing growth from within, but by augmentation of bulk through accretion of particles from without. (2) Minerals are not heterogeneous. While the objects treated of in the other departments of natural history consist of beings possessed of life, and having parts which, being mutually dependent, cannot be separated from one another without a more or less complete destruction of the individual, the objects treated of under the department of mineralogy have so uniformly consistent an individuality that they are not destroyed by any separation of parts,—each portion or fragment possessing the same properties and the same composition as the whole. And (3), while those beings which are possessed of life have their component elements grouped into complexes, for the most part capable of more or less freedom of motion and susceptible of change, minerals have a constitution resulting from chemical attractions alone and an arrangement of their parts, under physical influences, which has resulted in rigidity and an absence of all tendency to change.

Form of Minerals—Crystallography.

The most precise definition of a mineral would be—an inorganic body possessed of a definite chemical composition, and usually of a regular geometric form. Of these, the second is in one respect the direct outcome of the first; while many of the most important physical properties possessed by minerals are outcomes of the second.

Both the geometric form and the composition of minerals are produced and modified under the influence of general laws.

Mineral bodies occur in the three physical conditions of solid, liquid, and gas. Those now found in the last two states are few in number, and are of altogether inferior interest to those which occur as solids; but there is reason to believe that the minerals we know as solids once existed in the liquid or gaseous state, and that their present structure was determined in the process of solidification. All bodies thus formed may be divided into two great classes:—

1. Amorphous bodies, or such as do not possess a definite and characteristic geometrical form. These (when transparent) refract light singly in every direction (except when under stress); they are equally easy or equally difficult to break in all directions; when broken they exhibit a conchoidal or an earthy fracture; they are equally hard throughout all their parts; they are equally elastic in all directions; they conduct heat with equal rapidity and in equal amount in all directions.

2. Crystalline bodies, or such as occur in definite geometrical forms bounded by flat surfaces. These present greater facilities of separation of their particles, or “cleavage,” in certain directions lying in determinate planes than they do in others; most of them are neither equally hard nor equally elastic in all directions, conduct heat more rapidly in certain directions than they do in others, and, when transparent, refract light doubly except in certain directions.

Mineral bodies are found in both of the above classes; and the same mineral body may occur in both the amorphous and the crystalline condition. This is seen in the piece of gold shown in fig. 1, where the upper portion has a sharply angular and a well-defined shape, while the lower presents curvilinear and rugged outlines, similar to one another in no part. Under favouring circumstances, it is possible that every substance whose composition is capable of being represented by a definite chemical fornιula— i.e., which has an unvarying composition—may be capable of assuming a definite crystalline form.

Size and Form of Crystals.— They are of every size from over a yard in diameter to mere specks requiring a high power of the microscope to reveal their existence. Beryls have been obtained in America more than 4 feet in length by 2⅛ in thickness, weighing 2∣ tons. Equally large crystals of apatite have been found in Canada. There is a rock crystal at Milan 3} feet long by 5∣ in circumference, weighing 870 lb. The highest perfection of form, and hence of other properties, is only found, however, in crystals of moderate or of small size.

Variety of Form, and Constancy of Form.— The same mineral may be found in different localities, or sometimes in the same locality, exhibiting an almost endless variety of forms. Calc-spar occurs at a Scottish locality in acicular pyramidal crystals of which the length may be ten or more times as great as the width (fig.

2); in flat plates as thin as paper, in which the length is not the hundredth part of the width; also in prisms, pyramids, and rhombohedra, which at first sight (as in figs. 3, 4) seem destitute of any relationship to each other. This substance has elsewhere been noted in several hundred forms. The minerals fluorite, pyrite, and baryte have each been observed in over a hundred diverse forms. Nevertheless, however great the number, all the forms, in the case of each mineral, may be reduced or referred to a single type, by the simple process of examining its internal structure or the mode of arrangement of its molecules. This is accomplished in two ways—(l)by finding the weak joints in that arrangement, through splitting the crystal, and (2) by measuring the angular inclination of the outside surfaces which bound the form and, from these measurements, by simple mathematical laws, arriving at what has been termed its “primitive” or simplest form.

As regards the mere recognition of a substance, such measurement in itself suffices,—the angular inclination, if the same surfaces be measured, being unvarying in each species. It can, moreover, be shown that the possible range of external variety of form is governed by fixed mathematical laws, which determine precisely what crystalline forms are or may be produced for each species. Comparatively few of these actually occur in nature; but crystallographic laws can point out the range of those which can possibly occur, can delineate them even before they are found, and can in all cases show the relationship which subsists between them and the simple or fundamental form from which or out of which they all originate. It must be observed that in crystalline bodies the internal structure—that is, the arrangement of the molecules— is as regular in an outwardly shapeless mass as in the modelled crystal which presents itself as a perfect whole.

Definitions of Crystals, and their Members or Parts.— A crystal is a symmetrical solid, either opaque or transparent, contained within surfaces which theoretically are flat, and of a perfect polish, but which are actually frequently curved, striated, or pitted. These surfaces are called “planes,” or “faces.” The external planes of a crystal are called its “natural planes”; the flat surfaces obtained by splitting a crystal are called its “cleavage planes.” The intersections of the bounding planes are called “edges,” and planes are said to be similar when their corresponding edges are proportional and their corresponding angles equal. Crystals bounded by equal and similar faces are termed “simple forms.” The cube, bounded by six equal squares, the octahedron, bounded by eight equilateral triangles, and the rhombohedron, bounded by six equal rhombs, are thus simple forms. Crystals of which the faces are not all equal and similar are termed compound forms, or “combinations,” being regarded as produced by the union or combination of two or more simple forms. Edges are termed rectangular, obtuse, or acute, according as the angle at which the faces which form the edge meet is equal to, or greater or less than, a right angle. Edges are similar when the planes by the intersection of which they are formed are respectively equal and equally inclined to one another; otherwise they are unlike or dissimilar.

When a figure is bounded by only one set of planes, it is said to be “developed.” When an edge is cut off by a new plane, it is said to be “replaced”; when cut off by a plane which forms an equal angle with each of the original faces which formed the edge, it is said to be “truncated.” When an edge is cut off by two new faces equally inclined to the two original faces respectively, it is said to be “bevelled.” When a solid angle is cut off by a new face which forms equal angles with all the faces which went to form the solid angle, it is said to be truncated.

In classifying crystals and studying their properties, it is found convenient to introduce certain imaginary lines called “axes.” Axes are imaginary lines connecting points in the crystal which are diametrically opposite,— such as the centres of opposite faces, the apices of opposite solid angles, the centres of opposite edges. Different sets of axes may thus be drawn through the same crystal; but there is always one set, usually of three, but in one special class of crystals of four, axes, by reference to which the geometrical and physical properties of a crystal can be most simply explained. These axes intersect one another, either at right angles, producing “orthometric” forms, or at oblique angles, producing “clinometric” forms. The axes may be all equal, or only two equal, or all unequal.

There is a definite conventional position in which for purposes of description a crystal is always supposed to be held. With reference to this position one of the axes,— that which is erect or most erect,— is termed the “vertical,” and the others the “lateral.” The planes in which any two of the axes lie are called the “axial” or “diametral planes,”—sometimes “sections.” By these the space around the centre is divided into “sectants.” If there are, as is generally the case, only two lateral axes, the space is divided into eight sectants, or octants; but, if there are three lateral axes, it is divided into twelve sectants.

Primitive Forms of Crystals.— If we attempt to arrive, through a study of the internal structure of crystals, as evidenced by directions of weakness of cohesion, at the total number of primitive or parent forms which can exist, we find that there are thirteen such forms and no more.

Nine of these may be regarded as prisms standing upon a base, three as octahedra standing upon a solid angle; and tnere is one twelve-sided figure, or dodecahedron.

Prisms.— Of the prisms eight have a four-sided base

If the base is square and the prism stands erect—that is, if its sides or lateral planes, as they are called, are perpendicular to the base—the form is termed a “right square prism” (fig. 6). In this the four lateral planes are rectangular and equal; they may be either oblong or square; in the latter case the form is the “cube” (fig. δ). When the base is a rectangle instead of a square, the form is a “right rectangular prism’’ (fig. 7). In each of the above three forms the edges are twelve in number. In the cube all the edges are equal. In the square prism the lateral edges are all equal, but are different from the four equal edges of the base. In the rectangular prism, two at each base differ in length from the other two, while both differ from the lateral; hence there are here three sets of edges, four in each. In each of the three forms, however, the solid angles are eight in number, all equal, and each enclosed by three right angles.

When the base is a rhombus, and the prism stands erect, the form is a “right rhombic prism” (fig. 8). Two of the angles in the base being here acute and two obtuse, two of the solid angles corresponding each with each must differ from the others. So also must two of the lateral angles be acute and two obtuse.

The four lateral faces are equal.

When the base is a rhomboid, and the prism stands erect, it is only the opposite lateral faces that can be equal. The form is called a “right rhomboidal prism” (fig. 9).

When the base is a rhombus, but the prism stands obliquely on its base, the form is called an ‘ ‘ oblique rhombic prism” (fig. 10). Here the basal edges of the lateral planes are all equal in length, but on account of the inclination of the prism the angles which these edges form with the lateral edges of the lateral planes are two acute and two obtuse.

If all the edges of an oblique rhombic prism are equal in length to the breadth of the base, and if the lateral planes are rhombi equal in all respects to the basal, the form is called a“rhombohedron” (fig. 11). This is included within six equal planes, like the cube, but these planes have oblique angles. The rhombohedron thus bears the same relation to the oblique rhombic prism which the cube does to the right square prism. Of the eight solid angles of a rhombohedron only two are contained by three equal plane angles, and these two “apices,” as they may be called, are opposite one another. According as the apices are acute or obtuse, we have an acute or obtuse rhombohedron.

When the base of an oblique prism is a rhomboid, the prism becomes an “oblique rhomboidal prism” (fig. 12). In this form, only diagonally opposite edges are similar, as regards equality of length and the value of the included angle. Only opposite solid angles are equal, as are also the opposite and parallel faces.

A right prism may have an equilateral six-sided base; it is then called an “hexagonal prism.” This form may be developed in two positions relatively to each other, —one in which the transverse axes pass from the centres of opposite faces (fig. 13), the other in which they pass from the centres of opposite edges of the planes (fig. 14). The faces of the one set mutually truncate the edges of the other. If a rhombohedron be positioned so as to rest upon one of its apices, the faces of one hexagonal prism would truncate the lateral edges of the rhombohedron, while the faces of the other hexagonal prism would truncate its lateral solid angles. Hexagonal prisms may be longer or shorter than the width of their bases. The interfacial lateral angles are 120°. The angle between the lateral and terminal faces is 90°.

Octdhedra.— The planes of these eight-faced solids are triangular, and they may be regarded as made up of two four-sided pyramids applied to each other, base to base. They are always positioned so that they stand upon a solid angle with the “basal plane ”—that is, the plane which is the common base of the two pyramids—horizontal. In the primitive forms now under consideration the vertices of the two pyramids will in this position be vertically above and below the centre of the base. The upper and lower solid angles are then termed the “vertical solid angles,” and the four lateral solid angles are called the basal solid angles.

There are three octahedrons. In the “regular” octahedron (fig. 15) the base is a square, and the eight faces are equilateral triangles of equal size. There are twelve edges, which are all equal. The faces incline to each other at an angle of 109° 28' 16", and have the plane angles all 60°. There are six equal solid angles. When the base of the octahedron is square, but the other edges, although equal to one another, are either longer or shorter than the edges of the base, the form is a “right square octahedron” (fig. 16). In this the faces are isosceles triangles, the equal angles being at the basal edge of the planes. These basal edges are equal and similar, but differ in length and in angles from the eight equal pyramidal edges. When the base of an octahedron is a rhombus, it is called a “right rhombic octahedron” (fig. 17).

Dodecahedron.— This (fig. 18) has each of its twelve faces a rhombus. It is, like the cube and the octahedron, a solid which is symmetrical. The interfacial angles are all 120°, the plane angles are 109° 28' 16" and 70° 31' 44". The edges are twenty-four, and similar. There are fourteen solid angles, of which six are formed each by the meeting of four acute plane angles, and eight by the meeting of three obtuse plane angles.

It has been said that the above simple forms were arrived at through a study of the internal structure of crystals, chiefly as disclosed by cleavage. Inasmuch, however, as there are some minerals which cleave in only one direction, and many which cannot be cleaved in any direction, this method of investigation fails. Its employment, moreover, frequently led to conflicting or embarrassing results. A conflicting result is when a substance has more than one set of cleavages,—that is, splits up in directions which would result in the production of more than one of the above primary or simple forms. Thus the mineral fluorite occurs with much the greatest frequency in the form of the cube, and it might very consistently be held that its frequent occurrence in this form was a clear natural indication that the cube was the primary or simplest form of fluorite; but it splits up into an octahedron. Galena crystallizes frequently in the form of the octahedron; yet to cleavage galena yields a cubic primary form. It might be conceived that there had been, in each case, some special tendency to assume the cubic form and the octahedral form; but one and the same piece of rock may bear on its surface cubic crystals of fluor and octahedral crystals of galena, — each of the minerals having here assumed the primitive cleavage form of the other in preference to its own. The mineral blende crystallizes not unfrequently in octahedra, which yield the dodecahedron on cleavage. Fluor crystallizes in dodecahedra, yet yields the octahedron to cleavage. Argyrite crystallizes in cubes and in octahedra, but yields the dodecahedron on cleavage. Pyrite crystallizes in cubes, octahedra, and dodecahedra, and yields both the cube and the octahedron on cleavage.

These are most embarrassing results, but they clearly indicate so intimate a relationship to subsist between three of the above simple forms that it is obvious that one alone would serve as a type form for representing the others. The selection of that one should be based upon grounds of most eminent simplicity, and this again is to be arrived at by a consideration of the smallness of number of parts, i.e., of faces, edges, and solid angles. In such a consideration we find that the dodecahedron, with its higher number of each of these, at once gives place. The cube has six faces, the octahedron eight; simplicity here is in favour of the cube. The cube has twelve edges, the octahedron has twelve; in this respect they are equal. The cube has eight solid angles, the octahedron six; here the greater simplicity is on the side of the octahedron. So that this method of adjudicating by simplicity fails, and we are thrown back upon the relationships which may be unfolded through a consideration of the other elements of crystals,— their axes.

Systems of Crystals and Laws of Crystallization.

This consideration led, first, to the remarkable discovery that several of the above primary forms are mere modifications of each other, and ultimately showed that all crystals found in nature may be referred to six systems, based on certain relations of their axes, and that every face which could occur upon a crystal bears a definite and simple relation, in position and in angular inclination, to these axes.

As regards mere geometric measurement, there are several directions in which axes may with nearly equal advantage be projected. For example, in the cube (fig. 19) they may be drawn from the centres of opposite faces, as lettered O; or from opposite solid angles, as lettered C; or from the centres of opposite edges, as lettered D. There is abundance of evidence that each of these directions must be regarded as lines of dominant accretion of molecules.

But the accretion may be not only dominant but overwhelmingly so in one only of these directions in certain cases, or existent along one set of axes alone in certain others. In a specimen of native silver from Alva in Scotland (fig. 20), along O this is so much the case that the concreting molecules have done little more than delineate the form of an octahedron, and this they have only been able to do by aggregating themselves in lines of minute crystals of the very shape of which they were projecting the skeleton form. Moreover, a polar aggregation at the terminal ends of these octahedral axes is here shown by the amount of concreting and crystallizing material being larger at the terminations of these axes than elsewhere. In the hollow-faced cube again (fig. 21), an aggregation of molecules in the direction of the lines D and C has filled the edges and solid angles, while none have been deposited along 0.

This occurs in crystals of salt. In the hollow-faced octahedron, again (fig. 22), there has been no deposition of matter along the line C. Cuprite often shows this form; and it as frequently occurs in hollow-faced dodecahedra, wherein the vacuity is in the direction of D.

In the specimen of pyrite from Elba (fig. 23), a deposition along D and C would ultimately have erected the scaffolding of a hollθλv cube, in twelve lines of minute combinations of the cube and octahedron. Such directional arrangements may, moreover, not only be intermittent but often alternate. The pyrite from Traversella (fig. 24) is an illustration of the first. A large pentagonal dodecahedron having been completed, a new accession of material has been attached, not uniformly spread over the pre-existent crystal, to enlarge it, but locally arranged, in equal amount, at the poles of 0. But here the special method of the arrangement has determined the formation of a number of small crystals of the same form as that originally projected.

An alternation, as it were, in plan is shown in such a crystal of calcite as that in fig. 25. Here a scalenohedron is seen in the centre of the figure; then a rhombohedron has been perched upon its summit, and lastly both have been sheathed in a six-sided prism with trihedral summits. Different as these three forms are, it is found that they all here stand in a definite position one to the other; that definite position is the relation which they bear to one of the sets of axes, and this set may be assigned, not only to all the three crystals here combined, but also to all the crystals belonging to the same mineral, wherever occurring. This general applicability constitutes one of the respects in which one special set of axes is, in each of the systems, preferred to the others.

Another respect is the intensity with which the molecules cohere in the different parts of the crystal, as refeιτed to these axes, and the resultant different hardness of certain parts of crystals. It will be afterwards found that this obtains in a very limited manner in the crystals which belong to the first of the following systems, on account of its regularity and sameness as a whole. It may be laid down as a general rule that the edges of crystals are harder than the centres of their faces, and the solid angles harder than the edges. This is markedly the case in the diamond. But, apart from this, there is no distinctive hardness in any one part, side, or end of the crystals of the first system. It is otherwise with the crystals which fall to be considered in all the other systems. So different is the hardness of the various portions of these, so diverse the appearance of their parts in lustre, colour, polish, &c., so varying the amount of the recoil of these when struck, so unequal their power of conducting heat, so dissimilar their power of resisting the agencies of decay, and so irreconcilable their action upon transmitted light, that we cannot but conclude that the molecules which build them up are packed with greater force, if not in greater number, in certain directions in preference to others. There thus remains no question that these nature-indicated sets of axes are those along which there has been a specially selective or “polar” arrangement.

The six systems are founded upon the relationships of the axes in number, in length, and in angular inclination. All crystals may be divided into “orthometric” or erect forms and “clinometric” or inclined forms; and in similar manner may the systems be, through a consideration of the relative lengths of their axes, divided into three classes. In the first, or most regular, of these the axes are all equal, that is, they are of one length; in the second there is one axis which differs in length from the others, and therefore they are of two lengths; while in the third the axes are all unequal, and therefore they are of three lengths. Of the six systems one belongs to the first class, two to the second, and three to the third. Hence they are thus classed :— [table]

Though the grouping of the systems into three classes in virtue of axial dimensions is markedly borne out by optical and other properties, yet it is altogether insufficient for determining the relationships of the myriad forms in which bodies crystallize. Such knowledge is only attained by combining the consideration of axial length with axial inclination; and it is through a due regard of both of these that the six systems are instituted.

The above table may be read in two different ways,— either across or consecutively up and down the page. The six systems may be treated of in either of these ways; and there are certain advantages in considering them at least first by the former method.

We consider first, as the more essential, the relative lengths of the axes, and, secondly, the angular inclination of these.

1. In the cubic system the axes are all equal, and all intersect at right angles. Here is the most perfect simplicity, and the most perfect regularity.

2. In the tetragonal system two only of the axes are equal; but all still intersect at right angles. Here is a departure from simplicity as regards the length of one axis, but no departure as regards the angular inclination.

3. In the right prismatic system none of the axes are equal, but all still intersect at right angles. Here is total loss of regularity in the first particular, but still none in the second.

4. In the oblique prismatic system none of the axes are equal, and only two intersect at right angles. Here there is again a total loss of simplicity in the first particular, and a certain amount of departure from it in the second.

5. In the anorthic system none of the axes are equal, and none of them intersect at right angles,—so that here, as expressed by the name, there is a total departure from regularity in both particulars.

6. The hexagonal system is anomalous in relation to this mode of consideration. It is regarded as having four axes, three of which lie in one plane, parallel to the base, and intersect each other at equal angles

(necessarily angles of 60°). The fourth axis intersects these at right angles, and may be longer, shorter, or equal to them. This system is generally considered after the tetragonal system, as having one axis which differs in length from the others, and only one which cuts the others at right angles. By some a rhombohedron is considered as the primary of this system; it then comes to have three axes, all equal, but none intersecting at right angles.

In considering these systems, or in describing the form of a crystal, the vertical or erect axis is named the principal axis of the figure, and that axis is chosen as the vertical which is the only one of its kind. In the cubic system there is no such axis, so w that any one may be chosen as the vertical.

It will be convenient, before proceeding to the consideration of the laws of crystallography and the combinations of forms,—especially in view of the terminology that must be employed in illustrating those general aspects of the subject,—to give an outline of one of the six systems here. For this preliminary description the cubic system, as the simplest and most regular, naturally suggests itself as the most suitable.

I. The, Cubic System.— Here the axes are all equal, and all intersect at right angles. The “cube” (fig. 26), “octahedron” (fig. 30), and “rhombic dodecahedron” (fig. 33), which are here included, are alike in their perfect symmetry; the height, length, and breadth are equal; and their axes are equal, and are rectangular in their intersections.

In the cube (fig. 5) these axes connect the centres of opposite faces; in the octahedron (fig. 15) the apices of opposite solid angles; in the dodecahedron (fig. 18) the apices of opposite acute solid angles. The relation of these forms to each other, and the correspondence in their axes, will be made manifest through a consideration of the transition between the forms. If a cube be projected with the axes in the above position, or if a model of it in any sectile material be employed, and if the eight angles are sliced off evenly, keeping the planes thus formed equally inclined to the original faces, we first obtain the form in fig. 27, then that in fig. 28 and fig. 29, and finally a regular octahedron (fig. 30); and the last disappearing point of each face of the cube is the apex of each solid angle of the octahedron. Hence the axes of the former, being in no way displaced, necessarily connect the apices of the solid angles of the latter. By cutting off as evenly the twelve edges of another cube, the knife being equally inclined to the faces, we have the form in fig. 31, then fig. 32, and finally the rhombic dodecahedron (fig. 33), tvith the axes of the cube connecting the acute angles of the new form. These forms are thus mutually derivable. Moreover, they are often presented by the same mineral species, as is exemplified in galena, pyrites, and the diamond.

The process may be reversed, and the cube made from the octahedron, as will be readily understood from a comparison, in reverse order, of figs. 26 to 30. Or the cube may be similarly derived from the dodecahedron, as seen by inspecting figs. 33, 32, 31, 26.

The octahedron also is ι changed to a rhombic dodecahedron by removing its twelve edges (figs. 34, 35), and continuing the removal till the original faces are obliterated, thus producing the dodecahedron.

It will be observed that throughout all these changes the position of the axes, as determinants of dimensions, need not be altered,—that, in fact, one set of axes has served for all the forms.

The relationships of the principal forms of this system being thus disclosed, the forms themselves have next to be considered.

The cube (fig. 26) is bounded by six equal squares, has twelve edges formed by faces meeting at 90°, and eight solid trigonal angles. The axes are taken as joining the centres of each two opposite faces. Examples are hallite, galena, and fluor.

The octahedron (fig. 30), bounded by eight equilateral triangles, has twelve equal edges with planes meeting at 109° 28' 16", and six tetragonal angles. The principal axes join the opposite solid angles. Examples: magnetite, gold, cuprite.

The rhombic dodecahedron (fig. 33) is bounded by twelve equal and similar rhombi, has twenty-four equal edges oi 120°, and has six tetragonal and eight trigonal angles. Each of the principal axes joins two opposite tetragonal angles. Examples: garnet, cuprite, blende.

The tetrakishexahedrons (figs. 36, 37, 38, varieties of icositetrahedron) are bounded by twenty-four isosceles triangles, placed so as to form four-sided pyramids on the faces of the cube, arranged in six groups of four each. They have twelve longer edges, which correspond to those of the primitive or inscribed cube, and twenty-four shorter edges placed over each of its faces. The angles are eight hexagonal and six tetragonal, the latter joined two and two by the principal axes. Examples: fluorite, gold. This form varies much in general aspect. The four-sided pyramid which rests on the edges of each face of the cube may be so low as almost to fall into it (fig. 36); or it may rise so high that each side forms a level surface with that which is adjacent to it upon the nearest cubic face (fig. 38). In the latter case the form has become the rhombic dodecahedron; so that the more or less acute varieties of the form are but stages of a passage of the cube into the latter figure, through an increasing accretion of matter in the lines of the axes of the cube. This is termed a “transition by increment.”

The triakisoctahedrons, fig. 39 (variety of icositetrahedron, fig. 40), are bounded by twenty-four isosceles triangles, in eight groups of three, arranged as pyramids on the edges of the faces of the octahedron. Like the previous form they vary in general aspect, the variation here being from the octahedron on one side to the rhombic dodecahedron on the other; while the increased accretion here is in the direction of lines joining the centres of the faces of the octahedron or the solid angles of the cube. The passage of the forms is similar to that illustrated in the last-considered form. The edges are twelve longer, corresponding with those of the inscribed octahedron, and twenty-four shorter, three and three over each of the faces. The angles are eight trigonal and six ditetragonal (formed by eight faces), the latter angles joined two and two by the principal axes. Examples: galena, diamond.

The icositetrahedrons (fig. 40) are bounded by twenty-four deltoids. This form varies from the octahedron to the cube, sometimes approaching the former and sometimes the latter in general aspect. A four-sided pyramid rests on the angles of the faces of the cube. When increased accretion takes place along the cubic axes, an octahedron results. When it is along lines joining the solid angles of the cube, that form itself results. The edges are twenty-four longer and twenty-four shorter. The solid angles are six tetragonal joined by the principal axes, eight trigonal, and twelve rhombic or tetragonal with unequal angles. Examples: analcime, garnet.

The hexakisoctahedrons (fig. 41), bounded by forty-eight scalene triangles, vary much in general aspect, approaching more or less to all the preceding forms, into all of which they may pass; but most frequently they have the faces arranged either in six groups of eight on the faces of the cube, or eight of six on the faces of the octahedron, or twelve of four on the faces of the dodecahedron. There are twenty-four long edges, often corresponding to those of the rhombic dodecahedron or bisecting the long diagonal of the trapezohedron, twenty-four intermediate edges lying in pairs over each edge of the inscribed octahedron, and twenty-four short edges in pairs over the edges of the inscribed cube. There are six ditetragonal angles joined by the principal axes, eight hexagonal, and twelve rhombic angles. Examples: diamond, fluorite.

General Laws of Crystallography.— The seven forms of crystals now described are related to each other in the most intimate manner. This will appear more distinctly from the account which is to follow of the mode of derivation of the forms, with which is conjoined an explanation of the crystallographic signs or symbols by which they are designated. These symbols were introduced by Naumann, in the belief that they not only mark the forms in a greatly abbreviated manner, but also exhibit the relations of the forms and combinations in a way which words could hardly accomplish. In order to follow out this derivation of forms, it is necessary to state briefly the following laws, which have been established in crystallography. It is to be remembered that these laws apply, not merely to the cubic system just described, but to all the systems.

1. The Law of the Invariability of the Angles of Crystals, which was established by Romé de 1’Isle, may be thus stated :—the angles of inclination of the faces of a crystal are constant, however unequally the faces may be developed. The corresponding angles of different crystalline specimens of the same body do not, however, always absolutely agree. Differences have been found, amounting sometimes even to 10'.

2. The Law of Symmetry, discovered by Haiiy, may be thus expressed :—(1) similar parts of crystals—faces, edges, angles, and consequently axes—are all modified in the same manner, and dissimilar parts are modified separately or differently; (2) the modifications produce the same effect on the faces or edges which form the modified part, when they are equal; when they are not equal, they produce a different effect. That is, if an edge be truncated or bevelled, every similar edge will be similarly truncated or bevelled; if an angle be truncated or acuminated, every similar angle will be similarly truncated or acuminated; and consequently every similar axis will be equally affected by the modifications. Thus the cube has eight similar angles and twelve similar edges. In the physical production of the cube, if one of the angles or edges be modified, all will be similarly modified. This, which is the most important law of crystallography, is, however, subject to an exception which was fully formulated by Weiss. The law was—all the similar parts of crystals, faces, edges, angles, and consequently axes, are modified at the same time and in the same manner; the forms resulting from this law are termed “holohedral.” The exception is that half of them or one-fourth of them only may be similarly modified. When only half of the similar parts are modified, we get the “hemihedral” forms; when one-fourth only are modified, which occurs only rarely, we get “tetartohedral” forms.

3. The Law of the Parallelism of the Faces of a Crystal, discovered by Romé de 1’Isle, may be expressed as follows :—every face of a crystal has a similar face parallel to it; or every figure is bounded by pairs of parallel faces (with the exception of certain hemihedral forms).

4. The Law of Zones, first established by Weiss, may be thus enunciated :—the lines in which several faces of a crystal intersect each other (or would do so if they were produced until they met) frequently form a system of parallels. Such a series of faces is termed a “zone.” Sometimes the zones are parallel to one of the symmetrical axes. Thus, in every prism, the -faces of the prism constitute a zone which encircles the axis of the prism. Faces may be in a zone although they do not actually intersect on the form.

5. The Law of the Rationality of the Parameters of the faces of crystalline series, first indicated by Malus, is that the position of planes may be assigned by numbers bearing some simple ratio to the relative lengths of the axes of the crystal. This law was the outcome of investigations into the relationship of forms glanced at in commencing the consideration of the cubic system, and was arrived at through the study of the mode of derivation of forms.

The derivation of forms is that process hy which, from one form chosen for the purpose, and considered as the type,—the fundamental or primary form,—all the other forms of a system may be produced, according to fixed principles or general laws. In order to understand this process or method of derivation, it must be noted that the position of any plane is fixed when the position of any three points in it, not all in one straight line, is known. To determine the position, therefore, of the face of a crystal, it is only necessary to know the distance of three points in it from the centre of the crystal, which is the point in which the axes intersect each other. As the planes of all crystals are referred to their axes, the points in which the face (or its supposed extension) meets the three axes of the crystal are chosen, and the portions of the axes between these points and the centre are named parameters of the face; and the position of the face is sufficiently known when the relative length or proportion of these parameters is ascertained. When the position of one face of a simple form is thus fixed or described, all the other faces of the form are in like manner fixed in accordance with law 2, since they are all equal and similar, and have equal parameters—that is, intersect the axis in the same proportions. Hence the expression which marks or describes one face marks and describes the whole figure, with all its faces.

The octahedron is adopted as the primary or fundamental form of the cubic system, and distinguished by the first letter of the name, 0. Its faces cut the half-axes at equal distances from the centre; so that these semiaxes, the parameters of the faces, have to each other the proportion 1:1:1. In order to derive the other forms from the octahedron, the following construction is employed.

Suppose a plane to be laid down perpendicular to one axis, and consequently parallel to the two other axes (or to cut them at an infinite distance, expressed by ∞, the sign of infinity); then the hexahedron or cube is produced, designated by the crystallographic sign ooO∞,—expressing the proportion of the parameters of its faces, or oo: 1: ∞. If a plane is supposed placed on each edge, parallel to one axis, and cutting the two other axes at equal distances, the resulting figure is the rhombic dodecahedron, designated by the sign ooθ, the proportion of the parameters of its faces being oo: 1: 1. The triakisoctahedron arises when, on each edge of the octahedron, planes are placed cutting the axis not belonging to that edge at a distance from the centre m, which is a rational number greater than 1. The proportion of its parameters is therefore m:l : 1, and its sign mθ ; the most common varieties are ⅞0, 20, and 30, seen in diamond and fluorite. When, on the other hand, from a similar distance m in each two semiaxes prolonged a plane is drawn to the other semiaxis, or to each angle, an icositetrahedron is formed; the parameters of its faces have consequently the proportion m: m : 1, and its sign is mθm ; the most common varieties are 202 and 303,—the former very frequent in leucite, analcime, and garnet, the latter in gold and amalgam. When, again, planes are drawn from each angle, or the end of one semiaxis of the octahedron, parallel to a second axis, and cutting the third at a distance n, greater thanl, then the tetrakishexahedron is formed; the parameter of its faces is ∞: n: 1; its sign is ooOn; and the most common varieties in nature are ∞0f, ∞02, and oo03. Finally, if in each semiaxis of the octahedron two distances m and n be taken, each greater than 1, and m also greater than n, and planes be drawn from each angle to these points, so that the two planes lying over each edge cut the second semiaxis belonging to that edge at the smaller distance n, and the third axis at the greater distance m, then the hexakisoctahedron is produced; the parameters are m : n : 1, its sign mθn, and the most common varieties 30⅜, 402, and 50∣, seen in diamond and fluorite.

It must be observed that the numbers in the above signs refer to the parameters of the faces,—not to the axes of the crystal, which are always equal. One parameter also has always been, in the above, assumed =1, and then, either one only of the two other parameters, marked by the number before 0, or both of them, marked by the numbers before and after 0, have been changed.

In the above consideration of the mode of derivation of these forms actually found in nature, which belong to the cubic system, it will be observed (though the illustrations were limited) that the value of m and n in these indicated, by the precision of the proportions ⅞, 2, or 3, a definite numerical relationship. This at once led up to the extended observations which established the law above stated of proportionality in the modification of crystals, or the rationality of the parameters, which gives a mathematical basis to the science, adding to symmetry of arrangement a numerical relation in the position of the planes.

To illustrate this in a general form (and not merely with special reference to the mode of notation or expression of Naumann, which is that adopted in the subsequent descriptions), let A0A', BOB', COC' (fig. 42) be the three axes of a crystal, drawn in perspective, and cutting one another in the centre 0. The semiaxes OA, OB, 00 are three parameters. Now in the line OA take 0α 2 =⅜0A, and 0α s =⅛0A,—making as many points as may be necessary between OA, rational fractions of OA. Subdivide OB and OC in a similar manner. Further produce OA, OB, OC to Ao, Bo, Co, in each direction to an infinite distance, or to a supposed infinite distance, as expressed by the arrow-head; and suppose these extended axes to be divided in a manner similar to the subdivisions of the parameters, by rational multiples of OA, OB, and OC. All the planes of a crystal will be parallel to one or other of the planes which pass through three of the points thus determined.

First, in order to apprehend the relationship of faces to these axes, or to the half axes,—the parameters of the faces,—let us suppose one plane of a crystal to be so situated as to cut the three parameters OA, OB, OC at their extremities A, B, C, which it must be remembered are points equidistant from the centre; or let it be supposed that a glass plate rests upon three intersecting wires at such points. It is evident that such a plane or plate will have a definite inclination or slope. Suppose further a second plane or plate to exist, which cuts the three semiaxes in the points α 2 , ⅛ ⅜ which have been measured off (along with α 1 , b 1 , c 1 ) as equidistant from O. It will be evident that such a plane, though smaller, will be parallel to the first, seeing that, like it, it cuts the three parameters at equal distances from 0.

A little consideration will show that, whatever the absolute distances from the centre may be, so long as the supporting subdivisions are equal, no new slope of the glass plates or planes is possible; planes so situated must be parallel and similar. Any sign which may be adopted to express the slope of one of such planes must be applicable to all. A plane, however, cutting the points α 1 , ft 1 , c 2 will have quite a different slope.

Let us now suppose a plane to cut a different set of the semiaxes, namely, 0A', OB', 0C', in the points -α 1 , -b x , -c l . Such a plane would be parallel to one cutting the points - α 2 , - b 2 , - c 2 , and also to the set of planes first described, but on the opposite side of the centre of the crystal. If again, however, we had a plane cutting the semiaxes 0A' and OB' in - α 1 , - δ 1 , but the semiaxis 00' in the point - c 2 , it is clear that the slope of this plane would be quite different from that of the planes just described, but it would be parallel to the plane cutting the points a x , b x , c 2 . This slope, like the other, evidently depends, not on the absolute lengths of the portions of 0A', OB', 0C , cut off, but upon their proportions or ratios; and such is the case with all the planes which are referred to the same axes.

As there are three axes, and each or all of them may be cut at any points and at any ratios, it is evident that the number of planes which is possible is infinite; and it must be also evident that the inclinations of all are fixed or determinate if we know the ratios. While, however, the possible number of planes is infinite, the actual number occurring among minerals is either small or moderate, in virtue of the fact that the ratios of subdivision of the axes are always simple, and not numerous.

Naumann’s symbols for the notation or individualizing of planes have been glanced at. A simpler method is that of employing as indices the denominators (if simple fractions) of the fractional parts of the axis cut. Thus 111 is used for any plane parallel to that cutting the axes in a 1 , b x , c x ; 122 for those parallel to α 1 , b 2 , c 2 ; 313 for a 3 , b 1 , c 3 ; and so on.

When any of the points referred to have negative signs, the corresponding indices have negative signs placed over them. Thus 122 is the index for a plane parallel to a' x b 2 c 2 . 103 is the index of the plane α' 1 , b∞, c ’ 3 . oo here indicates infinity; that is, the plane never would cut the axis B however far it were extended; in other words, it is parallel to it. The necessity for elongating the axes is brought about by the occurrence of highly acuminating planes, which in many cases would not meet the axes at all unless these were prolonged.

If the axes are unequal, as in the trimetric forms, then the ratio is of the same character, except that the relative lengths of the axes come into consideration; but here, as in the regular system, irrational values cannot occur, and in even the most complex crystals they seldom exceed seven, either as aliquot parts or multiples.

It will thus be seen that in crystals there is no haphazard scattering of faces, but a complete subserviency to law, a law which may be said to be the linear equivalent to the law of multiple proportions by weight, and Gay Lussac’s law of multiple proportions in combination by volume.

In abbreviation of all the systematic modes of notation, letters of the Latin and Greek alphabets are frequently employed in a more or less arbitrary manner, and·with advantage in the case of highly complex forms.

6. The. Law of Symmetry of Crystalline Combination is the consequence of the law of symmetry and the law of the rationality of the parameters, and has been partially stated in enunciating these laws. It is thus expressed ·

(1) a substance can only crystallize in forms, whether simple or compound, which have the same relative symmetry, that is, belong to the same crystalline system, and the parameters of the faces of which bear a simple relation to each other, that is, belong to the same axis; (2) a form cannot be modified by faces belonging to a different system, or a different series.

Certain exceptions to the first part of this law occur. The element carbon occurs as the diamond, which is cubic, and as graphite, which is hexagonal. Sulphur occurs near volcanoes in needle crystals belonging to the oblique prismatic system, and also in caves (deposited apparently from solution) in crystals belonging to the right prismatic system. Titanic acid is tetragonal in rutile, and right prismatic in brookite. Carbonate of lime is hexagonal in calcite, and prismatic in aragonite. These are probably only apparent exceptions. The elementary substances which go to form them occur in different allotropic states, with different amounts of specific heat; and it is probable that in these different states they go to form the above modifications, which are therefore, in every respect, except in their chemical composition, different mineral bodies. The physical differences between diamond and graphite may suffice as an illustration. The diamond is transparent, colourless, brittle, and extremely hard; graphite is opaque, black, tough, and so soft as to be utilized as a lubricant.

Spheres of Projection.— The foregoing scheme for the development of the relation which subsists between faces of crystals and their axes affords but slight aid in displaying the position of the faces, or their mutual relationships. The delineation even of a considerable series of crystal forms does not indeed go far in effecting this,—on account, first, of very unequal development in the size of the faces of crystals, and, secondly, on account of the habit of development of these faces not only differing largely, but being special to certain localities,—as in the entire absence of some faces, and in the preponderance of others.

Maps of the whole domain occupied by the forms of each mineral have been happily projected for such display. The projection is laid down as on a globe, in accordance with stereographic projection, and admitting of calculation according to the laws of spherical trigonometry. These globe maps are called “spheres of projection.” The centre O is the common centre of the crystal and of the sphere in which the axes intersect. The three axes will of course meet the circumference of the sphere in six points, called the “poles of the axes.” From the centre radii are supposed to be drawn, meeting each plane perpendicularly. It is evident that such radü will have fixed inclinations to each other. They are called “normals” to the planes, and the points in which when produced they meet the circumference of the sphere of projection are called the “poles” of the corresponding faces. A face and its pole thus call for only one symbol. The angle included by any two normals is the supplement of that included by the two corresponding faces.

It is thus easy to determine the angles of any two normals when that of the corresponding faces is known, or vice versa. Thus, if the angle between two faces is 125°, that of the normals will be 55°. The spheres of projection are specially adapted to enable us to avail ourselves of the aid to calculation afforded by the forenoted fact that sets of faces lie parallel to each other, forming zones; for, when < projected on such a sphere, the normals of the parallel faces will all lie in one plane; and the poles, all cutting its surface in the direction of one line, may be connected, and so form a great circle on the sphere. This is called the “zone circle.” A line drawn through the cen⅛e of the zone plane, cutting it at right angles, is the “zone axis”; it is parallel to all the faces, and intersections of the faces (if they are extended enough to intersect), of the zone. A face may be common to two or more zones; its normals will then coincide with the intersections of the several zone planes.

In the absence of actual spheres upon which to detail the facts which go to form the “sphere of projection” of each substance, the hemisphere is represented on a plane surface. This has of necessity the disadvantage, except as regards the circumferential zone, of introducing spherical distancedistortion—foreshortening of all parts lying near the circumference; but the eye soon gets accustomed to this. Fig. 43 presents the principal zones of the cubic system, and shows the position of the poles of the faces of the cube, the octahedron, and the rhombic dodecahedron, o 1 , o 2 , o 3 , &c., are the poles of the octahedral faces; α 1 , ct 2 , α 3 , <fcc., those of the faces of the cube; and d v d 2 , d 3 , <fcc., those of the rhombic dodecahedron. It will be observed that the faces of the cube fall into the zone circles of the octahedron and dodecahedron, while those of the octahedron fall into those of the rhombic dodecahedron. Considering this as a delineation of a globe, these zone circles come to represent latitude and longitude; and, as almost all the faces in this system fall into some zone circle, it is clear that the latitude and longitude of all normals may be readily laid down, and their relations at once determined by spherical trigonometry Fig. 44 shows the arrangement of tho poles of all the forms belonging to the cubic system noticed above, or referred to in the present article,—delineated on an octant of the sphere of projection. It displays the perfect regularity of the system.

Hemihedral and Tetartohedral Forms.— The exception to the second law (that of symmetry), which was formulated by Weiss, was to the effect that one-half or even one-fourth only of the faces which go to form t: holohedral crystal may be present. When but one-half of the faces present themselves, the form is termed hemihedral; when only one-fourth, it is tetartohedral. These restrained developments have now to be considered. In hemihedral forms the development is restrained, but symmetry is not deranged; half the similar parts are still alike, though unlike the other half.

There are two classes of hemihedral forms :—

I. Those forms in which half the similar angles or edges are modified independently of the other half (“hemi-holohedral ”), producing—

1. In the monometric and dimetric systems ‘ tetrahedral” and “sphenoidal” forms, by the independent replacement of the alternate angles; their opposite faces are not parallel, and they are hence called “inclined” hemihedrons; as in chalcopyrite, boracite. 1 The replacement in the dimetric system of two opposite basal edges at one base and the other two at the opposite base is of the same kind; as in edingtonite.

2. In the trimetric system “monoclinic” forms, by the replacement of half the similar parts of one base and the diagonally opposite of the other, unlike the other half; as in datholite, humite.

3. In the trimetric and hexagonal systems “hemimorphic” ιorms, by independent replacements at the opposite extremities of the crystal; as in topaz, calamine, tourmaline.

4. In the rhombohedral system, by the replacements of the alternate basal edges or angles of the rhombohedron, forms usually called “tetartohedral” or quarter forms, on the ground that mathematically the rhombohedron is a hemihedral form derived from the hexagonal prism, which is the type of the hexagonal system. Rock crystal is usually developed according to this law.

II. Those forms in which all the similar angles or edges are modified, but by half the full or normal number of planes (“holo-hemihedral”), producing—

1. In the nιonometric system “pyritohedral” forms, by a replace, ment of the edges or angles; as in pyrites. Such forms have opposite faces parallel, and are often called parallel hemihedrons.

2. In the dimetric system “pyramidal” and “scalenoidal” forms, by a replacement of the eight solid angles of the primary prism, according to two methods.

3. In the hexagonal system “pyramoidal ’ ' and “gyroidal” forms, by a replacement of the solid angles of the hexagonal prism, or of the six lateral angles of the rhombohedron, according to two methods; as in quartz and apatite.

The above illustrations show that hemihedrism is not only divided into two classes, but is of various kinds, and these have been systematized as follows:—“holomorphic,” in which the occurring planes pertain equally to the upper and lower (or opposite) ranges of sectants, as in ordinary hemihedrons; and (2) “hemimorphic,” in which each set of planes pertains to either the upper or the lower range, but not to both. As to the relative position of the sectants which contain the planes, the forms may be vertically direct, as in baryte; vertically alternate, as in the tetrahedron, the rhombohedron, and the plagihedral faces of quartz; and vertically oblique, as in many forms of chondrodite.

In hemimorphic forms symmetry is deranged; the crystals are bounded at the opposite ends of their main axes by faces belonging to distinct formε or modifications,—always, however, of the same system; hence only the upper or the under half of each crystal can be regarded as complete, as regards the form there seen; and so for each end it is half formed.

Fig. 45 represents a crystal of tourmaline, which is bounded on the upper end by the planes of the rhombohedrons R (P) and - 2R (o), and on the lower end by the basal pinacoid (k ’ ). In fig. 46 of smithsonite the upper extremity shows the base k, two brachydomes o and p, and two macrodomes m and Z; 1 As the parts of either half are alternate, there still results a symmetrical solid. As either one or other half may be the one thus modified, there may result two such symmetric solids, which stand in an inverse position to one another. When the modifications affect the upper righthand solid angle, the resulting form is called +; when the upper lefthand angle it is -.

whilst on the lower end it is bounded by the faces P of the primary alone.

It has been found that all hemimorphic crystals become electrically polar when heated, that is, exhibit opposite kinds of electricity at opposite ends of the crystal. The subject will be more fully considered under the electricity of minerals.

The hemihedral forms of the cubic system are the following :—

1. The tetrahedron (fig. 47), hemihedral of the octahedron, is bounded by four equilateral triangles. It has six equal edges with faces meeting at 70° 32', and four trigonal angles. The principal axes join the middle points of each two opposite edges. Examples: fahlore, boracite, and helvine.

2. The trigonal dodecahedrons (fig. 48), hemihedral of the icositetrahedron, are bounded by twelve isosceles triangles, and vary in general form from the tetrahedron to the cube. There are six longer edges corresponding to those of the inscribed tetrahedron, and twelve shorter, placed three and three over each of its faces, and four hexagonal and four trigonal angles. Example: tetrahedrite.

3. The deltoid dodecahedrons (fig. 49), hemihedral of the triakis∙ octahedron, are bounded by twelve deltoids, and vary in general form from the tetrahedron on the one hand to the rhombic dodecahedron on the other. They have twelve longer edges lying in pairs over the edges of the inscribed tetrahedron, and twelve shorter edges, three and three over each of its faces. There are six tetragonal (rhombic), four acute trigonal, and four obtuse trigonal angles. The principal axes join, two and two, opposite rhombic angles. Example: tetrahedrite.

4. The hexakistetrahedrons (fig. 50), hemihedral of the hexakisoctahedron, are bounded by twenty-four scalene triangles, and most commonly have their faces grouped in four systems of six each. The edges are twelve shorter and twelve longer, lying in groups of three over each face of the inscribed tetrahedron, and twelve intermediate in pairs over its edges. The angles are six rhombic, joined in pairs by the principal axes, and four acuter and four obtuser hexagonal angles. Example: diamond.

In these forms, often named “tetrahedral,” the faces are oblique to each other. Their derivation and signs are as follows. The tetrahedron arises when four alternate faces of the octahedron, two opposite above and two intermediate below, are enlarged so as to obliterate the other four; and its sign is hence -. But, as either

2

four faces may be thus enlarged or obliterated, two tetrahedrons can be formed, similar in all respects except in position, and together making up the octahedron. These are distinguished by the signs + and -, added to the above symbol, but only the latter in general expressed, thus - - . In all hemihedric systems two forms similarly related occur, which may thus be named complementary forms. The trigonal dodecahedron is derived from the icositetrahedron by the expansion of the alternate trigonal groups of faces, τx . . τnθτn ., , ... 202

Its sign is — s - , the most common variety being — h - . The deltoid dodecahedron is in like manner the result of the increase of the alternate trigonal groups of faces of the triakisoctahedron, and its sign is . Lastly, the hexakistetrahedron arises in the development of alternate hexagonal groups of faces in the he∑a-kisoctahedron, and its sign is -9 n #

2

Two semitesseral forms with parallel faces occur. (1) The pentagonal dodecahedrons (fig. 51), bounded by twelve symmetrical pentagons, vary in general aspect between the cube and the rhombic dodecahedron. They have six regular (and in general longer) edges, lying over the faces of the inscribed cube, and twenty-

four, generally shorter (seldom longer), edges, usually lying in pairs oyer its edges. The solid angles are eight of three equal interfacial angles, and twelve of three interfacial angles, of which only two are equal. Each principal axis unites two opposite regular edges. This form is derived from the tetrakishexahedron, and its s ⅛ n is —2~ · It is found frequently in iron pyrites and cobaltine. (2) The dyakisdodecahedron (fig. 52), bounded by twenty-four trapezoids with two sides equal, has twelve short, twelve long, and twenty-four intermediate edges. The angles are six equiangular rhombic, united in pairs by the principal axes, eight trigonal, and twenty-four irregular tetragonal angles. It is derived from the hexakisoctahedron, and its sign is , the brackets being used to distinguish it from the hexakistetrahedron, also derived from the same primary form. It occurs in iron pyrites and cobaltine. The two other semitesseral forms, the pentagonal dodecahedron (fig. 53), and the pentagonal icositetrahedron (fig. 54), both bounded by irregular pentagons, have not yet been observed in nature.

Combinations.— The above-mentioned forms of the tessera! system (and this is true also of the five other systems of crystallization) not only occur singly, but often two, three, or more occur united in the same crystal, forming what are named combinations.

In this case it is evident that no one of the individual forms can be complete, because the faces of one form must interfere with, by diminishing, the faces of other forms. A combination therefore implies that the faces of one form shall appear symmetrically disposed between the faces of other forms, and consequently take the place of certain of their edges and angles. These edges and angles are thus, as it were, cut off, and a greater number of new ones produced in their place, which properly belong neither to the one form nor the other, but are angles of combination. These new faces are hence termed modifications, and the original or primary or simple form is said to be modified. Usually one form predominates more than the others, or has more influence on the general aspect of the crystal, and hence is distinguished as the predominant form, the others being considered subordinate.

The sign of the combination consists of those of its constituent forms, written in the order of their influence or importance in the combination, with a point between each pair.

It will be readily seen that such combinations may be exceedingly numerous, or rather infinite; and only a few of the more common can be noticed. Many others more complicated will occur in the descriptive part of this article. Among holohedral combinations, the cube, octahedron, and rhombic dodecahedron are the predominant forms. In fig. 27 the cube has its angles replaced by the faces of the octahedron, which truncate the angles, and the sign of this combination is 00O∞, 0. In fig. 28 this process may be regarded as having proceeded still farther, so that the faces of the octahedron nearly equal those of the cube, while in fig. 29 they now predominate; the sign, still of the same two elements, but in reverse order, is 0, ooθ∞. It will thus be seen that, through an increase in the amount of the abstraction of the faces of the cube, the figure gradually passes over into that of the octahedron. This may occur in all cases, and is termed the passage of the cube into the octahedron (or vice versa), or a “transition by decrement.”

In fig. 31 the cube has its edges replaced by the faces of the rhombic dodecahedron, which truncate the edges, the sign being οοΟοο,οοΟ; while in fig. 32 there is the same combination, nut with the faces of the cube subordinate, and hence the sign is ooθ, ooθ∞. The former figure, it will be seen, has more the general aspect of the cube, the latter of the dodecahedron. Here the solid angles of the latter are truncated by the faces of the cube, and we have the passage of the cube into the dodecahedron by decrement. The same transition, through truncation or decrement, could be shown in all cases of combinations, and in both directions, the last stage of the passage into one or other form always consisting of the replacement of its solid or interfacial angles by faces of the departing figure, more or less minute. A few illustrations of this may be given, in the three most important forms.

The relationship of the tetrakishexahedron to the cube has above been stated to be, that its faces form six low quadrilateral pyramids, which rest upon or spring from the edges of the cube. (From this the form derives its trivial name of four-faced cube.) Hence these faces bevel the edges of the cube. The first stage of such bevelling (or the last stage of the truncation of the tetrakishexahedron by the faces of the cube—whichever way it may be regarded) is seen in fig. 55. As the cubic face is here dominant, the sign is ooθ∞, ∞03. Fig. 56 shows a somewhat similar stage in the modification produced through the combination of the icositetrahedron with the cube. The trilateral pyramid which this form places upon the faces of the cube rests upon its solid angles, instead of, as in the last case, upon its edges’; hence it is these solid angles which, in the process of decrement, it replaces by faces which form a low three-sided pyramid. The triakisoctahedron, again, modifies the solid angles of the cube, as shown in fig. 57, by a low three-sided pyramid, positioned at right angles to that considered in the last combination. As the hexakisoctahedron is merely the two-faced form of that last considered, the pyramid which modifies the solid angles is, in its combination with the βube, six-sided, as in fig. 58.

As the faces of the rhombic dodecahedron truncate the edges of the octahedron, fig. 34 represents the first stage of such truncation or combination; while fig. 35 may be taken as representing the last, the faces of the octahedron being there nearly totally removed.

Fig. 59 shows the first stage of the passage of the octahedron into the icositetrahedron, in the truncation of the solid angles of the former form by a four-sided pyra mid formed by the (6 × 4) faces of the latter. The faces of the octahedron truncate the three-faced solid angles of the rhombic dodecahedron. Fig. 35 shows the first stage of this truncation, while fig. 34 shows an advanced amount. The faces of the icosi tetrahedron truncate the edges of the rhombic dodecahedron, as in fig. 60; while those of the latter truncate the unequal-angled tetragonal (or rhombic) angles of the former (fig. 61). The faces of the hexakisoctahedron bevel the edges of the ι¾ombic dodecahedron.

While such transitions may appear indefinite, yet certain minerals have either in themselves a habit, or have at certain localities a habit, of crystallizing so markedly in a certain stage of these transitions as to be absolutely capable of recognition thereby.

Combinations of hemihedral or, as they have been called, semitesseral forms are of three classes :—those with holohedral forms, those in which the faces fall obliquely on one another, and those with parallel faces. Fig. 62 shows the combination of a right-

handed tetrahedron with the cube, which truncates its edges, the tetrahedron here being dominant. Fig. 63, again, shows a combination of the cubo-dodecahedron with a right-handed tetrahedron, the first or holohedral form being in this case markedly dominant.

Fig. 64 is an illustration of the second class, combinations of oblique-faced semitesseral forms with each other. In it a right-handed tetrahedron has its solid angles truncated by the faces of one which is left-handed; and so its sign is 2- , - -2 . Fig. 65 2 2

shows a combination of a right-handed tetrahedron with a left handed three-faced tetrahedron. Fig. 66 shows a combination of a right-handed hemihedron of the icositetrahedron with a right-handed tetrahedron.

Parallel-faced hemihedrons generally form combinations with holohedral forms; and the amount of relative dominance is of all degrees. Fig. 67 shows a combination, in equal amount, of the cube with a vertical-faced pentagonal dodecahedron; while fig. 68 shows an increase in the amount of truncation effected by the latter. Fig. 69 shows the combination of the cube with the dyakidodecahedron, the former being dominant. In fig. 70 an octahedron, in dominance, is combined with the vertical-faced pentagonal dodecahedron: in fig. 71 the faces of these forms are of nearly equal size, while in fig. 72 the octahedral faces are nearly removed. The solid angles of the octahedron are modified in fig. 73 by the faces of the dyakisdodecahedron. In fig. 68 a vertical-faced pentagonal dodeca hedron is the prevailing form in combination with the cube; while in fig. 74 the faces of the octahedron are superadded. In fig. 75 its octahedral angles are modified by the faces of the icositetrahedron,

In each of the five systems which follow there is this difference from the cubic system that one axis is always unequal to (longer or shorter than) the others. This is placed erect, and named the chief axis; its ends are poles, and the edges connected with them polar edges. The other axes are named subordinate or lateral axes, and the plane that passes through them is the base. A plane through the chief and a lateral axis is a normal chief section. In these systems also occur the three forms of “pyramids,” “prisms,” and “pinacoids.” (1) The pyramids have their faces triangles. Pyramids in crystallography are each composed of two geometric pyramids placed base to base, and named “closed forms,” as the crystals are shut in by definite faces on every side. (2) The prisms are bounded by plane faces parallel to one axis. They are thus of unlimited extent in the direction of that axis, and therefore named “open forms,’’but in solid crystals are shut in by faces of other forms. (3) The pinacoids, or tables, have two faces intersecting one axis and parallel to the others, and thus are also open forms, or unlimited in the direction of these axes. Forms (2) and (3), when conjoined, mutually shut in each other, or produce closed forms.

II. Pyramidal or Tetragonal System.— This system has three axes at right angles, two of them equal, and the chief axis longer or shorter. The name tetragonal is derived from the form of the base, which is usually quadrangular.

There are eight tetragonal forms, of which five are closed. (1) Tetragonal pyramids (figs. 78, 79) are enclosed by eight isosceles triangles, with four middle edges all in one plane, and eight polar edges. There are three kinds of this form, distinguished by the position of the lateral axes. In the first these axes unite the opposite angles; in the second they intersect the middle edges equally; and in the third they lie in an intermediate position, or divide these edges unequally,— the last being hemihcdral forms. These pyramids are also distinguished as obtuse (fig. 78) or acute (fig. 79), according as the vertical angle is greater or less than in the regular octahedron. (2) Ditetragonal pyramids (fig. 80) are bounded by sixteen scalene triangles, whose base-lines are all in one plane. This form rarely occurs except in combinations. (3) Tetragonal sphenoids (fig. 81), bounded by four isosceles triangles, are the hemihedral forms of the first variety of tetragonal pyramids. (4) The tetragonal scalenohedron (fig. 82), bounded by eight scalene triangles, whose bases rise and fall in a zigzag line, is the hemihedral form of the ditetragonal pyramid. Nos. (3) and (4) are rare. (5) The tetragonal trapezohedron is not found in minerals as a simple form. The three open forms are—(1) tetragonal prisms, bounded by four planes parallel to the principal axis, which may be either longer (fig. 83) or shorter (fig. 84) than the lateral axes; (2) ditetragonal prisms, bounded by eight similar planes; and (3) the basal pinacoid, consisting merely of two parallel faces bounding the prisms at the ends, above and below. . , j r

The various series of tetragonal crystals are distinguished from eneh other onlv bv their relative dimensions. To determine these, one of the series must be chosen as the primary form, and for this purpose a tetragonal pyramid of the first variety, designated by P as ns sign, is selected. The angle of one of its edges, especially the middle edge, found by measurement, determines its angular dimensions, whilst the proportion of the principal axis a to the

Now if m be any (rational) number, either less or greater than unity, and if from any distance ma in the principal axis planes be drawn to the middle edge of P, then new tetragonal pyramids of the first order, but more or less acute or obtuse than P, are formed. The general sign of these pyramids is τnP, and the most common varieties ⅜P, 2P, and 3P,—with the chief axis half, twice, or thrice that of P. If m becomes infinite, then the pyramid passes into a prism, indefinitely extended along the principal axis, and with the sign oo P. If τn = O, which is the case when the lateral axes are supposed infinite, then it becomes a pinacoid, consisting properly of two basal faces open towards the lateral axes, and designated by the sign OP. Theditetra-gonal pyramids are produced by taking in each lateral axis distances n greater than 1, and drawing two planes to these points from each of the intermediate polar edges. The parameters of these planes are therefore m : 1: n, and the general sign of the form τnPn, the most common values of n being ⅜, 2, 3, and oo. When n=∞, a tetragonal pyramid of the second order arises, designated generally by mP∞ , the most common in the mineral kingdom being P∞ and 2P∞. The relation of these to pyramids of the first order is shown in fig. 85, where ABBBC is the first and ACCCX the second order of pyramid. In like manner, from the prism ∞P, the ditetragonal prisms ao^Pn are derived, and, finally, when n≈∞ the tetragonal prism of the second order, whose sign is ooPoo.

The combinations of the tetragonal system are either holohedral or hemihedral; but the latter are rare. Prisms and pinacoids must always be terminated on the open sides by other forms. Thus in fig. 86 a square prism of the first order is terminated by the primary pyramid, and has its lateral angles again replaced by another more acute pyramid of the second order, so that its sign is ooP, P, 2P∞.

In fig. 87 a prism of the second order is first bounded by the fundamental pyramid, and then has its edges of combination replaced by a ditetragonal pyramid; its sign is ooPoo, P, 3P3. In fig. 88 the polar edges of the pyramid are replaced by another pyramid, its sign being P, Poo. In fig. 89 a hemihedric form, very characteristic of chalcopyrite, is represented,—P and P' being the two sphenoids, a the basal pinacoid, and b, c two ditetragonal pyramids.

III. The Hexagonal System.— The essential character of this system is that it has four axes,—three equal lateral axes intersecting each other in one plane at 60°, and one principal axis at right angles to these. The plane through the lateral axes, or the base, from its hexagonal form, gives the name to the system. As in the last system, its forms are either closed or open. They are divided into holohedral, hemihedral, and tetartohedral,—the last, which are rare, having only a fourth part of the faces developed. Only a few of the more common forms require to be here described.

The hexagonal pyramids (figs. 90, 91) are bounded by twelve isosceles triangles, and are of three kinds, according as the lateral axes fall in the angles, in the middle of the lateral edges, or in another point of these edges, the last being hemihedral forms. They are also classed as acute or obtuse, but without any precise limits. The trigonal pyramid is bounded by six triangles, and may be viewed as the hemihedral form of the hexagonal. The dihexagonal pyramid is bounded by twenty-four scalene triangles, but has never been observed alone, and rarely even in combinations. The more common prisms are the hexagonal of six sides; in these the vertical axis may be either longer than the lateral, as in fig. 92, or shorter, as in fig. 93. There are also dihexagonal, of twelve sides.

A particular pyramid P is chosen as the fundamental form of this system, and its dimensions determined either from the proportion of the lateral to the principal axis (1: a) or from the measurement of its angles. From this form (τnP) others are derived exactly as in the tetragonal system. Thus dihexagonal pyramids are produced with the general sign wιPn, the chief peculiarity being that, whereas in the tetragonal system n might have any rational value from 1 to oo, in the hexagonal system it can only vary from 1 to 2, in consequence of the geometric character of the figure. When n=2, the dihexagonal changes into an hexagonal pyramid of the second order, whose sign is ?nP2. When m = oo , various prisms arise from similar changes in the value of τι; and when m — 0 the basal pinacoid is formed.

Few hexagonal mineral species form perfect holohedral combinations. Though quartz and apatite appear as such, yet properly the former is a tetartohedral, the latter a hemihedral species. In holohedral species the predominant faces are usually those of the hexagonal prisms ooP (fig. 92) and α>P2, or of the pinacoid OP (fig. 93); whilst the pyramids P and 2P2 are the most common subordinate forms. Fig. 94 represents the prism, bounded on the extremities by two pyramids,—one, P, forming the apex, the other, 2P2, the rhombic faces on the angles, or α>P, P, 2P2. Fig. 95 is a similar form, the upper part of the pyramid being replaced by the pinacoid. In some crystals the lateral edges of the prism are replaced by the second prism ∞P2 (fig. 96), producing an equiangular twelve-sided prism, which always represents the combination ∞P, <x>P2, and cannot occur as a simple form. Figs. 97, 98 are combinations in this system seen in beryl. An example of a more complicated combination is seen in fig. 99, of a crystal of apatite, whose sign with the corresponding lettersis ooP(J∕), ∞P2(e), 0P(P), ⅛P(r), P(χ), 2P(z). P2(α), 2P2(s), 4P2(d).

Hexagonal minerals frequently crystallize in those series of hemihedral forms that are named “rhombohedral,” from the prevalence in them of rhombohedrons. These (figs. 100, 101) are bounded by six rhombi, whose lateral edges do not lie in one plane, but rise and fall in a zigzag manner. The principal axis unites the two trigonal angles, formed by three equal plane angles; and in the most common variety the secondary axes join the middle points of two opposite edges. When the polar edges form an angle of more than 90°, the rhombohedrons are named obtuse; when of less than 90°, acute; fig. 102 represents the first, fig.

103 the second. Hexagonal scalenohedrons (fig. 104) are bounded by twelve scalene triangles, whose lateral edges do not lie in one plane. The principal axis joins the two hexagonal angles, and the secondary axis the middle points of two opposite lateral edges.

The rhombohedron is derived from the first order of hexagonal pyramid by the hemihedral development of its alternate faces. Its general sign should therefore be; but on several grounds it is ** found better to designate it by R or wιR, and its complementary figure by - mR. When the prism or pinacoid arises as its limiting form, they are designated by ooR and OR, though in no respect changed from the limiting forms ®P and 0P of the pyramid. The scalenohedron is properly the hemihedral form of the dihexagonal pyramid, but is more easily understood as derived from the inscribed rhombohedron mR. If the halves of the principal axis of this be multiplied by a definite number n, and then planes be drawn from the extremities of this enlarged axis to the lateral edges of the rhombohedron, as in fig. 105, the scalenohedron is constructed. It is now designated by mR» (the n on the right here referring to the chief axis), and the dihexagonal prism in this series by ∞Rn (formerly mR" and ooR n ).

The combinations of rhombohedral forms are very numerous, several hundreds having been described in calc-spar alone. Among the most common is the prism in combination with a rhombohedron, as seen in the twin crystal of calcspar (fig. 106), with the sign » R, - ⅛R, the lower ħalt being the same form with the upper, but turned round 180°. In fig. 107 the rhombohedron wιRhas its polar edges replaced by another rhombohedron - ⅜τnR, and in fig. 108 its lateral edges bevelled by the scalenohedron mRn. A more complex combination of five forms is represented in the crystal of calcspar fig. 109, its sign, with the letters on the faces, being R δ (ι∕),

IV. Right Prismatic or Rhombic System.— This system is characterized by three unequal axes, all at right angles to each other. Any one of these may be assumed as the chief axis, when the others are named subordinate. The plane passing through the secondary axes, or the base, forms a rhombus, and from this one of its names is derived. As prismatic forms are most frequent (the prism standing vertically on the rhombic base), it is best defined as the right prismatic. This system comprises only a few varieties of forms that are essentially distinct, and its relations are consequently very simple.

There are two closed forms. (1) The rhombic pyramids (figs. 110, 111), bounded by eight scalene triangles, whose lateral edges lie in one plane, and form a rhombus. They have eight polar edges (four acute and four more obtuse) and four lateral edges. The angles are six rhombic, the most acute at the extremities of the longest axis. (2) The rhombic sphenoids (figs. 112, 113) are bounded by four scalene triangles, with their lateral edges not in one plane, and are hemihedral forms of the rhombic pyramid. They are of very infrequent occurrence. The open forms, again, are rhombic prisms bounded by four planes parallel to one of the axes, which is indefinitely extended, and may be longer than the lateral, as in fig. 114, or shorter as in fig. 115. They are divided into upright (as in the above figs.) and horizontal prisms, according as either the principal or one or other of the lateral axes is supposed to become infinite. For the latter form the name doma or dome has been used; and two kinds, the macrodome (fig. 116) and the brachydome (fig.

117), have been distinguished.

. Rhombic pinacoids also arise when one axis becomes = 0 and the two others are indefinitely extended; and so we have macropinacoids (fig. 118) and brachypinacoids (fig. 119),—the qualifying term thus designating the axis to which the faces of the dome or pinacoid are parallel.

In deriving these forms from a primary, a particular rhombic pyramid P is chosen, and its dimensions determined either from the angular measurement of two of its edges, or by the linear proportion of its axes a: b : c, the greater lateral axis b being assumed equal to 1. To the greater lateral axis the name macrodiagonal is given, to the shorter that of brachydiagonal; and the two principal sections are in like manner named macrodiagonal and brachydiagonal, according to the axis they intersect. The same terms are applied throughout all the derived forms. They consequently mark only the position of the faces in respect to the axes of the fundamental crystal, and frequently of necessity without reference to the relative magnitude of the derived axes.

By multiplying the principal axis by any rational number m, greater or less than 1, a series of pyramids arise, whose general sign is mP, and their limits are the prism and pinacoid; the whole series being contained in this formula, OP . . . . wιP . . . . P . . . . mP .... ooP,—which is the fundamental series, the lateral axes always remaining unchanged.

From each member a new series may, however, be developed in two directions, by increasing one or other of the lateral axes. When the macrodiagonal is thus multiplied by any number n greater than 1, and planes drawn from the distance n to the polar edges, a new pyramid is produced, named a macropyramid, with the sign mPn, the mark over the P pointing out the axis enlarged. When n=oo, a macrodome results, with the sign mP∞. If the shorter axis is multiplied, then brachy-pyramids and brachydomes are produced, with the signs mPn and mPoo. So also from the prism ∞P, on the one side, originate numerous macroprisms oopn, with the limiting macropinacoid ooPα>; on the other, numerous brachy-prisms ∞Pn, with the limit form ooP<x>, or the brachypinacoid. In figs. 120, 121 the two domes are shown in their relation to the primitive pyramid.

The pyramids seldom occur independent, or even as the predominant forms in a combination; sulphur, however, is an exception. Prisms or pinacoids usually give the general character to the crystal, which then appears either in a columnar or tabular or even rectangular pyramidal form. The determination of the position of these crystals, as vertical or horizontal, depends on the choice of the chief axis of the fundamental form. In the topaz crystal (fig. 122) the brachyprism and the pyramid are the predominant elements, associated with the prism, its sign and letters being ooI>2(Z), P(o), ooP(jlf). Fig. 123 of stilbite is another example, the macropinacoid oo Poo or Μ being combined with the pyramid P(r), the brachypinacoid oofrx>(T), and the basal pinacoid 0P(P). Another instance is fig. 124 of a lievrite crystal, where the brachyprism and pyramid combine with the macrodome, or oof 2, P, Pα>. The above figures are very common forms of barytes,—figs. 125 and 126 being both composed of the pinacoid OP, a brachydome, and a macrodome, with sign 0P(c), f ∞ (∕), ⅜P∞ (d). The variation in aspect arises from the predominance of different faces; and fig. 127 consists of the macrodome ⅜Poo, the prism ooPtø), and the pinacoid OP.

V. The Oblique Prismatic System.— This system is characterized by three unequal axes, two of which intersect each other at an oblique angle, and are cut by the third at right angles. One of the oblique axes is chosen as the chief axis, and the other axes are then distinguished as the orthodiagonal (right-angled) and clinodiagonal (oblique-angled). The same terms are applied to the chief sections, and the name of the system refers to the fact that these two planes form with the base two right angles and one oblique angle C.

The forms of this system approach very near to those of the right prismatic series, but the inclination of the axis, even when almost a right angle, gives them a peculiar character, by which they are always readily distinguished. Each pyramid thus separates into two altogether independent forms or hemipyramids.

Three varieties of prism also occur—vertical, inclined, and Horizontal—with faces parallel to the chief axis, the clinodiagonal, or the orthodiagonal. The horizontal prisms, like the pyramids, separate into two independent partial forms named hemiprisms or hemidomes. The inclined prisms are often designated clinodomes, the term prism being restricted to the vertical forms. Orthopinacoids and clinopinacoids are also distinguished, from their position in relation to the axes. The monoclinic pyramids (fig. 128) are bounded by eight scalene triangles of two kinds, four and four only being similar. Their lateral edges lie all in one plane, and the similar triangles are placed in pairs on the clinodiagonal polar edges.

The two pairs in the acute angle between the orthodiagonal and basal sections are designated the positive hemipyramid, whilst the two pairs in the obtuse angles of the same sections form together the negative hemipyramid. But, as these hemipyramids are wholly independent of each other, they are rarely observed combined. More frequently each occurs alone, and then forms a prism-like figure, with faces parallel to the polar edges, and open at the extremities. Hence, like all prisms, they can only appear in combination with other forms. The vertical prisms are bounded by four equal faces parallel to the principal axis, and the cross section is a rhombus; the clinodomes have a similar form and section; whilst the horizontal prisms or domes have unequal faces, and their section is a rhomboid.

The mode of derivation of these forms closely resembles that of the rhombic series. A complete double pyramid is assumed as the fundamental form, and designated ±P, in order to express the two portions of which it consists. Its dimensions are given when the proportion of its axes a : δ: c and the angular inclination of the oblique axes C, which is also the inclination of the orthodiagonal section to the base, are known.

The fundamental series of forms is OP . . . . ±τnP . . . . ±P .... ±mP .... ooP, from each of whose members, by changing the dimensions of the other axes, new forms may be again derived. Thus from ±mP, by multiplying the orthodiagonal by any number n, a series of orthopyramids ±mP 0 τι is'produced, with the ortho, domes τnP c ∞ as limiting forms. The clinodiagonal produces a similar series of clinopyramids ±τnP c n, with the limiting clinodome mP c oo always completely formed, and therefore without the signs ± attached. From ooP arise orthoprisms ooP°n and the orthopinacoid ooP 0 oo, and clinoprisms ooP i ιι and the clinopinacoid ooP e oo. In these signs the o or c attached to the P indicates that the orthodiagonal (o) or clinodiagonal (c) axis has been multiplied. Formerly the latter forms were enclosed in brackets, thus (mP∞) =mPoo.

The combinations of this system may be easily understood from their resemblance to those of the right prismatic, the chief difficulty being in the occurrence of partial forms, which, however, closely resemble the hemihedral forms of the previous systems. A few examples only need therefore be given.

Fig. 129 represents a very common form of gypsum crystals, α>P c oo, (P), ooP(∕), P(Z). The most common form of augite is represented in fig. 130, with the sign ∞P(Λf), α>P o oo (r), ∞P e oo (I) , P(s ).

Fig. 131 is a crystal of common felspar or orthoclase, composed of the clinopinacoid ooP e oo(J∕), the prism ∞P(T), the basal pinacoid 0P(P), and the hemidomes 2P 0 ∞(y)∙, to which, in fig. 132 of the same mineral, the hemipyramid P(o) and the clinodome 2P c ∞ (n) are added.

VI. Anorthic or Triclinic System.— This is the least regular system, and departs the most widely, indeed almost absolutely, from symmetry of form. The axes are all unequal, and inclined at angles none of which are right angles,—so that, to determine any crystal, or series of forms, the proportion of the axes a: b: c, and also their angles, or those of the inclination of the chief sections, must be known. As in the previous systems, one axis is chosen as the principal axis, and the two others distinguished as the macrodiagonal and brachydiagonal axes. In consequence of the oblique position of the principal sections, this system consists entirely of partial forms wholly independent of each other, and each composed only of two parallel faces. The complete pyramid is thus broken up into four distinct quarter-pyramids, and the prism into two hemiprisms. Each of these partial forms is thus nothing more than a pair of parallel planes, and the various forms consequently mere individual faces. This circumstance renders many triclinic crystals very unsymmetrical in appearance.

Triclinic pyramids (fig. 133) are bounded by eight triangles whose lateral edges lie in one plane. They are equal and parallel two and two to each other, each pair forming, as just stated, a tetartopyramid or open form, only limited by combination with other forms, or, as we may suppose, by the chief sections. The prisms are again either vertical or inclined; the latter are named domes, and their section is always rhomboidal. In deriving the forms, the fundamental pyramid is placed upright with its brachydiagonal axis to the spectator, and the partial forms designated, the two upper by 'P and P', the two lower by z P and P,, as in the figure. The further derivation now follows as in the right prismatic system, with the modifications already mentioned.

Some combinations of this system, as the series exhibited by most of the felspars, approach very near to the oblique prismatic svstem: whilst others, as cyanose and axinite, show great incompleteness and want of symmetry. In the latter case the determination of the forms is often difficult. In the albite crystal (figs. 134, 135) P is the basal pinacoid OP; Μ the brachydiagonal pinacoid oofoo; s the upper right pyramid P'; I the right hemiprism ooP'; T the left hemiprism ∞'P; and x the hemidome 'P'<x>. Figs. 136 and 137 are crystals of axinite, the former from Dauphine, the latter from Cornwall, of whose faces the following is the development :— r the macropinacoid α>Poo; P the left hemiprism oo'P; uthe left upper quarter-pyramid 'P; I the left upper quarterpyramid 2'P; s the left upper partial form of the macropyramid 3'P3; and x the hemidome 2'P'α>.

The Measurement of the Angles of Crystals.

The permanence of the angular dimensions of crystals shows the importance of some accurate method of measuring their angles,—that is, the inclination of two faces to each other. Instruments for this purpose are called goniometers.

Two have been specially used for this purpose—the common or contact goniometer, invented by Caringeau, and the reflecting goniometer of Wollaston. The former is simply two brass rulers turning on a common centre, between which the crystal is so placed that its faces coincide with the edges of the rulers, and the angle is then measured on a graduated arc. This instrument is sufficiently accurate for many purposes and for large crystals, but for precise determination is far inferior to the reflecting goniometer. This requires smooth and even faces, but these may be very small, even the hundredth of an inch; and, as small crystals are generally the most perfect, far greater accuracy can be attained.

The reflecting goniometer is represented in fig. 138. It consists essentially of a graduated circle mm, divided on its edge into twice 180°, or more frequently into half-degrees, the minutes being read off by the vernier hh. This circle turns on an axis connected with tt, so that by turning this the circle is moved round, but it is stopped at 180°, when moving in one direction, by a spring at k. The other part of the instrument is intended to attach and adjust the crystal to be measured. The first axis of mm is hollow, and a second axis, aa, passes through it from ss, so that this and all the connected parts from b to ∕ can be turned without moving the circle mm. The axis d passes through a hole in be, so that it can turn the arm de into any required position; f is a similar axis turning the arm og, and pq a fourth axis, in like manner movable in g, and with a small knob at q, to which the crystal to be measured is attached.

When about to be used, the instrument should be placed on a table, with its base horizontal (which is readily done by the screws in it), and opposite to a window at about 12 or 15 feet distance, so that its axis shall be parallel to the horizontal bars of the window. One of the upper bars of the window, and also the lower bar, or, instead of the latter, a white line on the floor or table parallel to the window, should then be chosen, in order to adjust the crystal. The observer places himself behind the instrument with the side a at his right hand. The crystal is then attached to g by a piece of wax, with the two faces to be measured upwards, ana the edge of union of the faces, including the angle to be measured, as nearly as possible in the line of aa. The eye being brought near to the first face of the crystal, the axes αα and p are turned till the image of the window is seen reflected in the face with the horizontal and vertical bars in their position. The axis d is then turned through a considerable angle (say 60°), and the image of the window again sought and brought into its proper place by turning the axis∕, without moving p. When this is done that face is brought into its true position, normal to d, so that no motion of d can disarrange it. Hence the image of the window may now be sought in the second face, and brought into its true position, with the horizontal bars seen horizontal, by moving the axes d and a. When this is done the crystal is properly “adjusted.” The angle is measured in the following manner. First bring the zero of the circle and vernier to coincide, and then turn the inner axis a or ss, and move the eye till the image of the upper bar of the window reflected from the more distant face of the crystal coincides with the lower bar or horizontal line seen directly. Keeping the eye in its place, turn the other axis tt till the reflected image of the upper bar in the other face in like manner coincides with the lower line; the angle of the two faces is then read off on the divided circle. As the angle measured is not directly that of the faces but of the rays of light reflected from them, or the difference between the angle wanted and 180°, the circle has the degrees numbered in the reverse direction, so as to give the angle without the trouble of subtracting the one from the other.

The apparatus figured is for adjusting the crystal, and is an improvement suggested by Naumann. In the original instrument the axis fo was made to push in or out in a sheath, and had a small brass plate, bent at right angles, inserted in a cleft at o, to which the crystal was attached. The crystal was adjusted as formerly by moving the plate, or the axis fo, and by slight motion of the arm de, which should be at right angles nearly to be when used. A very marked improvement is to have a small mirror fixed on the stand below the crystal, with its face parallel to the axis aa, and inclined at 45° to the window, when the lower line can be dispensed with, and the instrument used for various other purposes of angular measurement. Many more perfect instruments have been introduced for the purpose of insuring greater accuracy; but the simple instrument is sufficient for all purposes of determinative mineralogy, and the error from the instrument will, in most cases, be less than the actual variations in the angles of the crystals.

Departure from Geometric Simplicity and Loss of Regularity in Crystals.

Such departures may be regulated by law, or may result from an undue operation of the force of accretion in certain directions.

1. Regular Departures from Simplicity.— There are three varieties of this :—parallel groupings, twin forms, hemitrope forms.

Parallel Groupings.— A plurality of individuals are here arranged either so that a line which joins their centres becomes a prolongation of one or other of their crystallographic axes, or so that their axes are parallel.

Fig. 20 shows the first, where cohesion sufficient for stability requires that the minute octahedra must mutually penetrate somewhat into each other. Fig. 139 shows the same in baryte. If we suppose octahedra united, the upper left-hand face of the one with the lower right-hand face of the other, there would be parallelism of their axes. Re-entering angles would, in such cases, prove a plurality of individuals, but if a number of cubes were superimposed in similar position, no such angles would occur, an elongated square prism resulting; and such arrangements, if repeated, are linear, or, with diminishing size in the individual, acicular.

Twins and Hemitropes.— Though closely related, formed under the operation of very similar laws, and to a certain extent passing into one another, these are not the same. In the first case a plurality of individuals must be present; in the second this is not necessary. In fig. 140 two individuals evidently intersect one another; in figs. 141, 142 one individual may be supposed to have been bisected in a certain direction, and the two halves reattached, but in a position differing in some definite manner from their relative position before the separation.

There are four varieties of true twins: those of apposition, of intersection, of partial or completed interpenetration, and of incorporation.

The first is exemplified by spinel, as in fig. 143; the second by staurolite, as in fig. 144; the third by calcite, as in fig. 146, and by blende, as in fig. 145, where the two individuals of fig. 143 may be supposed to have been forced vertically into one another: and the last by quartz, as in fig. 147.

The following are the laws of union of twins. 1. The face of union of twins, termed the “face of composition,” must be either a plane which does occur in the mineral twinned, or which can occur in accordance with the fifth law of symmetry. A face of union in twins is also a face of union in hemitropes of the same mineral. 2. From the above it results that the axes of the united crystals are either parallel (fig. 148) or inclined (fig. 149). The former generally occur among hemihedric forms; and the two crystals are combined in the exact position in which they would be derived from or would reproduce the primary holohedral form. The class with oblique axes occur both in holohedric and in hemihedric forms; and the two individuals are then placed in perfect symmetry, in accordance with law 1.

Twins are generally recognized by having re-entering angles (figs. 150, 151); but sometimes the crossed faces coincide in one plane, when the combination appeal’s as a single individual (figs. 152, 153). The line of union may then be imperceptible, or it may be disclosed by the intersection of two sets of striae (figs. 154,155), or by some physical diversity in the characters of the two faces.

The formation of twin crystals may be again, or many times, repeated,—forming groups of three, four, twenty-four, or more. When the faces of union are parallel to each other, the crystals form rows of indeterminate extent. When they are not parallel, they may return into each other in circles, as in rutile; or form bouquet or rosette groups, as in chrysoberyl (fig. 156); or stellate groups, as in calcite (fig. 157) and in cerussite (figs. 158, 159).

When the crystals are of different size, greater complexity results; but a number of minute crystals are frequently arranged upon a larger at those points where the angles of a single large crystal would protrude. Occasionally a simple form is twinned with a more complex one, as in chabasite (fig. 160).

Hemitrope crystals we may imagine as having beep formed from a single crystal, which has been cut into two halves in a particular direction, and one half turned round 180°, or 90°, or 60°. The line about which the revolution is supposed to take place is called the “axis of revolution.” From the amount of turn usually being 180°, Haiiy gave the name hemitrope. The position of the two halves in this case resembles that of an object and its image in a mirror, whose surface then would represent the plane of reunion.

The following are the laws of hemitropes. The axis of revolution is always a possible crystallographic line,—either an axis, a line parallel to an axis, or a normal to a possible crystalline plane. The plane normal to the axis of revolution is called the twin plane; it is either an occurring or a possible plane, and usually one of the more frequently recurring planes. Both the axis and the twin plane bear the same relation to both halves of the crystal in their reversed positions; consequently the parts of hemitrope crystals are symmetrical with reference to the twin plane (except in triclinic forms and some hemihedral crystals). The face of composition very frequently coincides with the twin plane; when not coinciding, the twin plane and the face of composition are generally at right angles to each other, so that the composition face is parallel to the axis of revolution. But in twins of incorporation the surfaces of composition have exercised a disturbing influence on one another, so that the surface of union is exceedingly irregular. Still in these cases the axis and the plane of twinning retain a definite position; but the face of composition, being no longer defined, is useless as a determinant.

There are three modes in which the composition may take place in hemitropes. These may be explained by dividing a crystal into halves, with the plane of division vertical, and then turning one of the halves round.

I. One of the halves may be inverted, as if by revolution through 180° on a horizontal axis at right angles to the plane of section, and the two faces again united by the surfaces which were separated. Here the surfaces of union are the original ones, but the base of one of the halves has taken the place of its summit. Examples: selenite (fig. 161) and orthoclase.

2. One of the halves may be turned round through 180", as if by revolution on a horizontal axis, parallel to the plane of section, and the face opposite and parallel to that of the plane of section—an originally external face—may then be applied to the other half. Here, not only has the base of one-half become a summit, but a lateral and external face of the original crystal has been thrust to its centre so as to become a face of internal union. Example: labradorite (fig. 162).

3. One of the halves may be turned round through 180°, as if by revolution on a vertical axis, parallel to the plane of section, the external face opposite and parallel to the plane of section becoming a face of union. Here, however, both the original summits retain their position as summits. Example: orthoclase.

The first of these modes of composition may occur in each of the systems, but it is not always apparent until disclosed by optical properties. The second is rare, and the third still more so.

In hemitrope crystals (less frequently in true twins) the halves of the crystal are frequently reduced in thickness in the direction of the ordinary twin axis; and when there is a parallel repetition of hemitropes, which frequently occurs, they are often reduced to very thin plates, not the thickness of paper, giving to the surface of the aggregate a striated structure and appearanee.

In the cubic system the faces of composition, both of twinning and of hemitropic revolution, are those of the cube, the dodecahedron, and the octahedron.

In the first case we have the axes of the two crystals necessarily in some cases parallel, or, more correctly, falling into one; but, as in this system all the axes are alike, or all the cubic faces similar, composition may occur along or parallel to all alike, and double or triple twins occur. We have examples in twins of the pentagonal dodecahedron (fig. 163) made up by the interpenetration of a right and a left ( + and - ), and of the tetrahedron, as seen in pyrite and fahlerz respectively. In virtue of the position required by law 2, it will be seen that the position of the solid which is common to both intersecting crystals is in the twin of pyrite the four-faced cube, which is the holohedral form of the pentagonal dodecahedron, while in the case of the fahlerz twin (fig. 164), the common portion is an octahedron, the holohedral form of the tetrahedron.

Twinning on an octahedral face is seen in the apposition twin of spinel (fig. 143), the tetrahedral twin of blende (fig. 165), the interpenetrative octahedral twin of blende seen in fig. 166, and. the intersecting cubes of fluor (fig. 167).

This is also the usual twin face for hemitropes of the cubic system.

Itis seen in fig. 168 of blende, where the two parts of the rhombic dodecahedron are united by it. Magnetite, spinel, and diamond frequently occur in octahedral hemitropes of the same composition (fig. 169).

This is also the face of composition for tetartohedral hemitropes.

Fig. 170 is that of the diamond. Here six of the faces of the six faced octahedron, with six faces diagonally opposite, form a low double six-sided pyramid (a portion of an octahedral face truncating each) through an 180° revolution of one set of these. Garnet sometimes shows both twins and hemitropes of the dodecahedron, of dodecahedral composition.

In the tetragonal system, twin crystals are very uncommon, but hemitropes frequent. With parallel axes they very seldom occur, but are seen in chalcopyrite. When the axes are inclined, the plane of union is usually one of the faces of the primary pyramid; and, as these faces are all similar, composition may take place simultaneously parallel to all. Very complicated forms hence result, as seen in chalcopyrite and in cassiterite (fig. 171)∙

In cassiterite the plane of union is frequently one of the faces of the pyramid P∞, sometimes one of those faces that replace the polar edges of P (figs. 172 173). From the bend the latter form is termed geniculated.

Hausmannite occurs in hemitropes of the primary P; and on the polar edges of this other twins are symmetrically repeated, a central individual appearing like a support to the others (figs. 174, 175).

In the hexagonal system twins are very common among the rhombohedral (the hemihedral) and the tetartohedral forms; while hemitropes prevail among the hexagonal or holohedral forms. The twins are generally formed by the interpenetration of two rhombohedrons, a + and a -, the vertical axis being the axis of composition; as in chabasite (fig. 176), cinnabar, levyne, calcite, &c. Sometimes six or more crystals, united parallel to the prismatic planes, form rosettes; as in chabasite from Giant’s Causeway. The almost endless stellate forms of crystals of snow are built up in this manner. Many of the most beautiful combinations to be seen among crystals result from this mode of arrangement.

Parallel groupings of hexagonal prisms also occur, as in apatite (fig. 177).

Rock crystal, in consequence of the tetartohedral character of its crystallization, exhibits twins in which the double hexagonal pyramid P may be said to be separated into two rhombohedrons P and r; these, though geometrically similar, are physi cally distinct. In fig. 178 the two individuals have not entirely interpenetrated, and might be regarded as simply grown together with parallel axes; but in fig. 147 there is so complete an interpenetration that the composite character of the crystal is only evidenced through a difference in the character of the surfaces of the two halves, which are most irregularly disposed.

The hemitropes of this system often form regular crystals, when the two halves have been united by a plane parallel to the base, so as to appear like a simple crystal, as in fig. 179. Here each end shows the forms ooR, - ⅜R, but the terminal faces appear in parallel instead of alternate position. Something of the same is seen in fig. 180, a hemitrope scalenohedron from Derbyshire. Hemitropes with the face of the primitive rhombohedron as the face of composition are also common; and they are sometimes joined by a face of - ⅜R, the two axes forming an angle of 127° 34'. Occasionally a third individual is interposed in a lamellar form, as in fig. 181, where the faces of the two outer portions become parallel. This is found in some pieces of Iceland spar. When the crystals unite in a face of the primary rhombohedron, they form an angle of 89° 8'; hemitropes on this law are easily recognized by their differing so little from a right angle in the re-entering bend (figs. 182, 183).

The faces which in this species act as faces of composition are exceedingly numerous; other examples are figs. 142, 146, 148, and 149.

In the right prismatic system twin crystals with parallel axes are rare, but with oblique axes common, the faces of union being one of the faces of the prism α>P. Twins of this kind occur frequently in aragonite, cerussite, mispickel, and marcasite. In aragonite the crystals are partly interpenetrating, and partly merely in juxtaposition, as in fig. 184, where the individuals are formed by the combination ooP(J∕), ooPco(Λ), P∞(⅛). In fig. 185 several crystals of the same combination form a series with parallel planes of union, the inner members of which are often so shortened that they form mere films, which appear as striae on the faces P∞ and ooPα> of the twin.

In fig. 186 four crystals, each of the combination ooP, 2P∞, having united in inclined planes, form a circular group, which returns into itself. Cerussite occurs in similar groups, building up a composite hexagonal crystal. It also occurs in stellate twins of two or three individuals, as in figs. 158, 159. Similar stellate combinations are also common in chrysoberyl. In staurolite, individuals of the prismatic combination ooP, ot>Poo, OP combine, either as in fig. 144 by a face of the brachydome, having their chief axes almost at right angles, or as in fig. 140 by a face of the brachypyramid ⅞P⅜, the chief axes and the brachypinacoids (o) of each of the crystals meeting at an angle of about 60°. This mineral, which is very frequently twinned, also forms combinations with the axes parallel (fig. 187).

In the oblique prismatic system, twins are by no means so frequent as hemitropes. Twins of interpenetration with parallel axes, but the one turned as regards the other round a vertical axis, are common in orthoclase (figs. 188, 189). Such crystals are termed right-handed (fig. 188) and left-handed (fig. 189), according to the side of the crystal which has been turned. In this mineral hemitropes occur around an axis normal to Μ, to P, and to n (fig. 529); double twins of the last two are common (fig. 530).

Harmotome and phillipsite form first hemitropes, and then twins of these, which are arranged sometimes as crosses and sometimes as double crosses (fig. 190). In hemitropes of gypsum the two halves are united by a face parallel to the orthodiagonal section, as in fig. 161, where the two halves have united so regularly that the faces P ’, P form only one plane. In a similar manner the two halves of the augite crystal represented in fig.

130 are in fig. 191 united so perfectly and symmetrically that the line of junction cannot be observed on the clinopinacoid. The two hemipyramids P(s) (like - P (Z) in the gypsum crystal) form at one end of the crystal a re-entering, at the other a salient angle.

Hornblende (fig. 192) and wolfram exhibit a similar appearance. This results in the imparting a pseudo-hemimorphism to certain oblique prismatic twins, which is well seen in the twins of sphene (figs. 193 and 589), and in exalting the characteristic appearance of true hemimorphs, as seen in the twin of acmite (fig. 194). In other cases the individuals partially penetrate each other in the direction of the orthodiagonal. This mode of union is not uncommon in gypsum, and is very frequent in orthoclase. Two crystals of the latter of the combination (ooPo 0 ), ooP, OP, 2P∞ as in fig. 131, are often pushed into each other, as shown in fig. 195.

In the anorthic system some twin formations are of great importance, e.g., as a means of distinguishing the triclinic from the mono clinic species of felspar. In one variety the twin axis is the normal to the brachydiagonal chief section. But in the anorthic felspars this section is not perpendicular to the base, and consequently the two bases form on one side a re-entering, on the other a salient angle; whereas in the oblique prismatic felspars (where the brachydiagonal chief section corresponds to the clinodiagonal) no twin crystals can be produced in conformity to this law, and the two bases fall in one plane.

and P (as well as those of 'P'∞, or x and x'), are a very characteristic appearance, marking out this mineral at once as a triclinic species. Usually the twin formation is repeated, three or more crystals being combined, when those in the centre are reduced to mere plates. When very numerous, the surfaces P and x are covered with fine striae, often only perceptible with a microscope. A second law observed in triclinic felspars, particularly in albite and labradorite, is that the twin axis corresponds with that normal of the brachydiagonal which is situated in the plane of the base. In pericline, a variety of albite, these twins appear as in fig. 198, where the two crystals are united by a face of the basal pinacoid P, whilst the faces of the two brachypinacoids (Jf and AΓ) form edges with very obtuse angles (173° 22'), re-entering on the one side and salient on the other. These edges, or the line of junction between Μ and M', are also parallel to the edges formed by these faces and the base, or those between Μ and P. In this case also the twins are occasionally several times repeated, when the faces appear covered by fine striae.

Cause of the Fσrmation of Twins and Hemitropes.— It has been shown above that the relative position of the molecules of crystals is determined by a polarity in the molecules themselves. This polarity must exist along three lines which intersect in the centre of the molecules; and unlike poles must attract each other. It has been supposed that compound crystals result from a reversion of the original polarity of the molecules of a crystal, after it has attained ά certain size. Heat and electricity, resulting from movements in strata, might occasion such reversion during the formation.of a crystal, and this would suffice for the explanation of hemitropes, though not directly of geniculated crystals, and still less of intersecting twins. Twins have accordingly been divided into ‘ ‘ paragenetic” and “metagenetic.” The first term is applied to the ordinarily occurring twins, in which the compound structure is supposed to have had its beginning in a nucleal compound molecule, or to have been compound in its very origin. In metagenetic twins the crystal was at first simple, but afterwards, through some change in the material furnished for its increase or possibly induced in itself, it received new layers, or an extension in a reversed position.

Rutile occurs in crystals like fig. 173, but with a bend at both extremities, instead of one only. Here the middle portion of the crystal is supposed to have attained a length of half an inch, and then it became geniculated simultaneously at both extremities; indeed, in this mineral such geniculatione are frequently repeated until the ends are bent into one another, and produce short hexagonal prisms with central depressions or even vacuities. The repeated twinning which produces striation, as in calcite and the felspars, and the peculiar rippled structure of amethyst, are ascribed to a similar operation, acting in an oscillatory manner.

Certain intersecting twins in the cubic system may be explained simply through excessive or undue accretion of molecules along certain lines. At page 351 it was shown how the three-faced octahedron (fig. 39) was formed through an accretion of molecules upon the faces of the octahedron along axes joining the centres of its faces (those which connect the solid angles of the cube). It was also shown that when through this accretion two faces of the triakisoctahedron (fig. 199), adjacent along the edge of the octahedron, rose into one plane the rhombic dodecahedron resulted. If now accretion still goes on along the same axes, so that the trihedral pyramid rises above the level of the dodecahedral planes, fig. 200 results. This is the twin of the three-faced tetrahedron (fig. 201).

If the accretion is still along the same axes until the lateral edges of the adjacent pyramids fall into the same line, fig. 202 results; and this is the twin of the simple tetrahedron (fig. 203). Here accretion upon the faces of a complex holohedral form has produced a twin of a simple hemihedral form.

Again, starting from the six-faced octahedron (fig. 204), there is produced by the same process first fig. 205, the twin of the sixfaced tetrahedron (fig. 206), and ultimately fig. 207, the twin of the three-faced tetrahedron (fig. 208).

2. Departure, from, Regularity on Account of Undue Accretion in certain Directions.—Distortion of Crystals.— The laws of crystallization should produce crystal forms of perfect symmetry; these laws, however, are subject, not only to the influence of other laws, but also frequently to disturbing influences which are subject to no law. Absolute symmetry, therefore, is very uncommon, crystals being generally so distorted and disguised through interference during their formation that either familiarity on the one hand or skill on the other is necessary for their recognition. As the magnitude of the angles may vary somewhat, even this guide may sometimes perplex. Hence it is necessary to be familiar with such departures from symmetry; and some of the more common are here noticed.

In the cubic system a cube (fig. 26), lengthened or shortened along one axis, becomes a right square prism (fig. 209), and if elongated in the direction of two axes is changed to a rectangular prism (fig. 7). Cubes of pyrites, galena, fluor-spar, &c., are generally thus distorted. It is very unusual to find a cubic crystal that is a true symmetrical cube. In some species the cube or octahedron (or other monometric form) is lengthened into a capillary crystal or needle, as happens in red copper and pyrites. Crystals of acicular pyrites occur at the Newton-Stewart lead-mine.

An octahedron flattened parallel to two of its faces is reduced to a tabular crystal (fig. 210). If lengthened in the same direction, it takes the form in fig. 211; or if it is still further lengthened, to the obliteration of two opposite octahedral faces, it becomes an acute rhombohedron (same figure).

When an octahedron is extended in the direction of a line between two opposite edges, it has the general form of a rectangular octahedron; and still further extended, as in fig. 212, it is changed to a rhombic prism with dihedral summits. The figure repre- .

sents this prism lying on its acute edge (spinel, fluor,, magnetite).

The dodecahedron when lengthened in the direction of the upright axis becomes a square prism with pyramidal summits (fig. 213); and when shortened along the same axis it is reduced to a square octahedron with truncated basal angles (fig. 214). Both these forms are modifications of the square prism; the first mode of distortion is common in garnet, rendering it liable to be considered zircon; the second is seen in aplome, when it might be taken for stannite. When the first of these forms is flattened, as in fig. 215 it resembles a form of stilbite.

When a dodecahedron again is lengthened along a diagonal between the obtuse solid angles, it becomes a six-sided prism with trihedral summits, as in fig. 216; and when shortened in the same direction, it becomes a rhombohedron which has its six acute angles truncated (fig. 217). In the first case, a crystal of green garnet or uwarowite would resemble dioptase; in the latter, colourless garnet would resemble; calcite. ’

The trapezohedron is exceedingly subject to distortions which frequently disguise it much. When elongated in the direction of the upright axis it becomes a double eight-sided pyramid with four-sided summits (fig. 218); a further elongation along the same axis would result in the obliteration of these summit faces, and in the production of a perfect double octagonal pyramid (fig. 219). The first of these distortions is exceedingly common in analcime and not uncommon in garnet; the latter rarely occurs in analcime. Lengthened along an octahedral axis it becomes fig. 220; shortened along the same it becomes fig. 221. Both are seen in analcime.

When the tetrakishexahedron is lengthened along a single octahedral axis it assumes the form of fig. 222; still further elongated, with obliteration of one half of its planes, it becomes a scalene dodecahedron. resembling the “dog tooth” form of calcite (fig. 223). Fig. 224 is a hemihedron of this form, produced by shortening along an octahedral axis, with obliteration of all the planes which do not touch the poles of that axis.

In the case of modified crystals of this system the distortions are more complex. Fig. 225 represents a crystal of cinnamonstone from Aberdeenshire; it is a combination of the dodecahedron and the trapezohedron. Only four dodecahedral faces remain (<Z), and those of the trapezohedron (n) are of unequal size. It may be best understood by regarding it as fig. 218 with the four vertical faces of fig. 213; so that it combines the distortions of both of these figures.

Crystals of diamond are very frequently distorted, though generally through curvatures of their faces.

Imperfections in the Surfaces of Crystals.

Of these the most important are striae, caverns, and curvatures.

1. Striated Surfaces.— The parallel furrows on the surfaces of crystals are called striae, and such surfaces are said to be striated.

Each ridge on a striated surface is enclosed by two narrow planes. These planes often correspond in position to a secondary or to the primary planes of the crystal, and we may suppose these ridges to have been formed by repeated oscillation in the operation of those causes which give rise, when acting uninterruptedly, to larger planes. By this means the surfaces of a crystal are marked in parallel lines with a succession of narrow planes, meeting at angles alternately re-entering and salient, and constituting the ridges referred to. This combination of different planes in the formation of a surface has been termed an oscillation of faces.

Cubes of pyrites are generally striated in such a way that the striae on adjacent faces are at right angles to one another. These lines are parallel to the intersections of the primary faces with the planes of the pentagonal dodecahedron, which is the most common form of pyrites; and they have evidently resulted from an oscillation between the primary and this secondary form.

The rhombic dodecahedron is often striated parallel either with the edges, or with the longer or the shorter diagonal of its faces. In the first case, seen in garnet (fig. 226), there is a passage into the sixfaced octahedron; the second results from an oscillatory combination of the dodecahedron with the regular octahedron, as in magnetite; and the last with the cube, as in aplome.

Rhombohedrons of chabasite are often striated parallel to the terminal edges (fig. 227), indicating an oscillatory combination between the primary faces and a secondary plane which bevels these edges.

Striation of faces is more frequent in the rhombohedral system than in any of the others. Horizontal striae are of almost invariable occurrence in the prismatic faces of quartz, whatever be the form of the crystal. The oscillation here has taken place between the pyramidal and the prismatic faces (figs. 228, 229, 230). During its growth there seems to have been a continued effort to complete the crystal by the assumption of the terminal planes,—which effort was intermittently overcome by a preponderating one to continue the deposition of matter along its main axis. Quartz crystals, from these alternate efforts, often taper to a point, without having any regular pyramidal face.

Tho lateral planes of prisms of tourmaline are very frequently convex, owing to oscillation between several lateral faces. In all such cases the interfacial angles cannot be determined, as they are lost in the rounding.

The striations on the lateral faces of foliated minerals are merely the edges of laminae. Examples: mica and gypsum.

2. Cavernous Crystals.— Crystals not unfrequently occur with a deep pyramidal depression occupying the place of each plane, as is often observed in common salt, galena (fig. 21), and sulphur. In the solution of crystals through atmospheric exposure, an approach to the same form is sometimes obtained, owing to the fact that the centres of the faces yield sooner than the edges and angles. Crystals of redruthite are often thus cavernous. Sometimes octahedrons occur with a triangular cavity, in place of each face (fig. 22). The same is met with in other forms.

3. Curved Surfaces. — Curved surfaces sometimes result from the oscillatory combination already noticed. Otters result from a curvature in the laminae constituting the crystal. Crystals of diamond have convex faces, and are sometimes almost spheres. This mode of curvature, in which all the faces are equally convex, is less common than that in which a convex surface is opposite and parallel to a corresponding concave surface. Rhombohedrons of spathic iron and pearl spar are usually thus curved, as is shown in fig. 231. The saddle-shaped crystals of the same mineral (fig.

232) are remarkable instances of several reversed curvatures in the same face. A singular curvature is shown in fig. 233, of calcite. The conical crystals of brown zinc blende, and the lenticular and conical crystals of gypsum, are other examples. Crystals of quartz are sometimes curved and twisted. When this takes place in the left-handed and right-handed crystals, the twist is to the right or left according as the crystal is rightor left-handed.

The surfaces of crystals are frequently far from flat, on account of fracture, with dislocation of the several fragments, occasioned by motion in the enclosing rock, the material of which is forced, or it may be transfused, into the rents. The tourmalines and beryls (fig. 234) which occur in granitic dykes are very subject to this, the fragments being often bent as well as displaced. A more or less simultaneous effort in the crystallization of two substances may produce a structure with the external form of one, the interior of which exhibits imbedded crystals of the other, more or less perfect in their development. In pegmatite or graphic granite, rude crystals of felspar contain skeleton forms of quartz, of which generally only one side of the prism and two of the pyramid occur, forming a rude lettering. Similar hollow quartz forms occur imbedded in garnet, radiating from its centre (fig. 235), and roughening its surface from protrusion, without distorting its form. Totally imbedded microscopic crystals, “microliths,” are, as in the latter cases, chemically non-assimilable. These are frequently arranged in layers in the including crystal, as in augite and leucite. When there is a certain amount of chemical resemblance there may occur a definiteness in the arrangement; and if the enclosed substance crystallizes in a system differing from that of the mineral which includes it, the angles of the latter are more or less distorted. This is the case in “microcline,” where the intrusion of a plagioclastic felspar causes some departure from the rectangularity of orthoclase. Foreign amorphous matter caught up or attaching itself to the surfacer of a crystal, during the process of its growth, causes lines of feeble cohesion,—as in the case of capped crystals of quartz. Here an occasional selectiveness in the sets of faces to which the foreign matter adheres seems to indicate that it has been to some extent under the influence of a polarity in its adhesion. Something of the same kind seems to have influenced the arrangement of the quartz grains caught up during the formation of the crystal of garnet shown in fig. 236. The perfect modelling of rock crystals is, however, but little interfered with by the almost numberless substances which they contain.

Aggregation of Crystals.

Crystalline aggregates which pass into amorphous masses may, in their more marked or perfect form, be assigned to an imperfect twinning.

Crystals are often grouped in linear series, as in native copper and silver, and thus constitute long threads or reticulations. In clustered crystals those adjoining each other are generally parallel in position, and are united by a plane parallel to one of the principal sections, or to planes of common occurrence. Senarmont mentions a union in galena, parallel to the octahedral faces, as common; and he also describes an instance where the union was parallel to the plane 3∣.

The positions of crystals on the supporting rock seem at first to be without any regularity. But by closer inspection we detect even here the same law of harmony that governs the formation of the simple and compound crystal. The various positions assumed correspond generally with the more common kinds of composition in twin crystals. This regularity is not always manifest on account of the unevenness of the surface on which they rest. In general, however, on glancing over a surface covered with crystals, a reflexion from one face will be accompanied with reflexions from the corresponding face in each of the other crystals, showing that the crystals are similarly positioned throughout.

This tendency to parallelism in the positions of associated crystals is apparent even in crystalline aggregates. In granite, for example, which is composed of felspar, quartz, and mica, the felspar crystallizations have usually a common position; that is, the corresponding extremities lie in the same direction, or nearly so. On this account granite is cleavable in one direction more easily than in others, and this direction is that of the perfect cleavage plane of the felspar; the second less perfect cleavage of the felspar permits of fracture of the rock nearly at right angles to the first; but, as there is no such third cleavage in the felspar, the workman, in fashioning the blocks of granite for paving stones, is compelled to chip or dress them off in the third direction.

The dominant action of polarity may, moreover, give a parallel position to the main axes of different minerals belonging to the same system, when crystallizing in association, and even to those which belong to different systems. Fig. 237 is an illustration of the first of such cases, where a crystal of zircon is implanted into a crystal of xenotime, and has its main axis identically in the same line. As illustrations of the latter—a parallel position of the axes of crystals of different systems—there are records of such association in crystals of cyanite and staurolite, of muscovite and haughtonite, of albite and orthoclase. The same has been observed between crystals of rutile and specular iron,—the crystals of rutile in this case having the vertical axis in the direction of a lateral axis of the specular iron. Haidinger has observed pyroxene and hornblende crystals associated in parallel positions.

A prism of calcite terminating in the planes g (fig. 106) has been observed, in which each plane was covered with small crystals of quartz all lying symmetrically, with their pyramids pointing towards the summit of the calcite crystal. When one mineral is changed into another, a polarity of accretion is still often seen to have dominated in the arrangement. In a crystal of calcite which had been changed into a number of minute crystals of aragonite, the main axes of the latter all lay in the direction of the main axis of the original crystal of calcite.

Irregular Aggregation of Crystals.— Besides the regular unions now described, crystals are often aggregated in peculiar ways, to which no fixed laws can be assigned.

Thus some crystals, apparently simple, are composed of concentric crusts or shells, which may be removed one after the other, always leaving a smaller crystal like a kernel, with smooth distinct faces. Some specimens of quartz from Beeralston in Devonshire consist apparently of hollow hexagonal pyramids placed one within another. Other minerals, as fluor-spar, apatite, idocrase, heavy spar, and calc-spar, disclose a similar structure by bands of different colours. A growth rendered intermittent through the deposition of a thin layer of foreign matter is thus developed.

Many large crystals, again, appear like an aggregate of numerous small crystals, partly of the same partly of different forms. Thus some octahedrons of fluor-spar from Schlaggenwald are made up of small dark violet-blue cubes, whose projecting angles give a drusy character to the faces of the larger form. Such polysynthetic crystals, as they may be called, are very common in calc-spar.

Forms of Crystalline Aggregates.— Crystals have often been produced under conditions preventing the free development of their forms; and, according to the direction of the axis in which the development has been checked, they may be divided into “columnar” and “lamellar” arrangements.

The columnar structure is made up of a more or less fibrous arrangement; and this may be supposed to have accrued from the simultaneous growth of a multitude of crystals from a single or from closely adjacent centres of support, so that, while the crystals were free to elongate themselves in the direction of their main axis, their increase was restrained laterally, by their impact upon one another. When the surfaces of support are level, or consist of the opposing sides of a vein, the columns or fibres, frequently exceedingly delicate, are parallel, and not unfrequently they then have a silky lustre. In the latter of the above circumstances the fibres are disposed transversely to the vein. Examples: gypsum, chrysotile, satin-spar. When the surface of support is rough, or has angular projections, the fibres radiate from certain of these in all directions, producing, in a thin vein, a starlike form, whence the arrangement is called “stellular.” Example: wavellite. When this takes place in an open cavity, producing brush-like forms, they are termed “radiant.” Examples: antimonite, needlestone. When the points of divergent growth are so positioned that the radiating groups interlace with one another, the structure is said to be “reticulated,” from its resemblance to a net. Example: tremolite. When individual members of such fibrous structure project above the general surface with acuminated extremities, they are said to be “acicular”; when the protruding columns are of uniform thickness they are termed “bacillary,” or rod-like. Such terms as straight, curved, twisted-columnar, diverging, or confused-fibrous explain themselves. Such fibrous arrangements as the above may occur imbedded centrally in a rock mass, which had been the magma out of which they were formed; or they may line the inner surface of cavities, filled originally either with water or aqueous vapour. These modes of occurrence have been distinguished by Mohs as crystal groups and druses. The former includes all unions of imbedded crystals round a central nucleus; the latter those of crystals of simultaneous or regularly successive growth on a common support. In the first case, there may be spheroidal, ellipsoidal, cockscomb, or other forms, frequently seen in marcasite, pyrite, and gypsum. In the second, spheroidal forms are less rare, but are seen in the case of several of the fibrous zeolites. In such cases surfaces more or less rough are coated, and diminished in angularity, through the hemispherical forms produced by the radiation of a multitude of fibres. Certain imitative outlines thus result from the successive deposition of layers of these crystals. These forms or uniting masses are termed “globular” when nearly spherical, “botryoidal” when like bunches of grapes, “reniform” or kidney-shaped when the spheres are larger, more confluent, and less distinct, and “mammillated” when the masses are nearertohemispheres. Mesolite occurs in globular forms; prehnite in botryoidal; haematite and chalcedony in reniform; and siderite and calamine in mammillated. In all the above cases the transverse fracture of such structures discloses the fibrous arrangement of the parts; but, if the growth has been intermittent, lines of deposit, concentric with the central nucleus of each sphere, are evidenced by layers of distinct colours. Fracture or separation frequently takes place, also, along such lines. In such drusy cavities—termed “geodes” when they are circular— after a certain number of such lines of deposit, grouped arrangements which have somewhat more of free crystalline development may assume other imitative forms in which there is a certain dependence on the crystallographic character of the mineral concerned. There are thus produced coralloidal or coral-like groups, fruticose or cauliflower-like groups, capillary or hair-like, and filiform or thread-like or wire-like forms. Often these groups expand in several directions, and produce arborescent, dendritic, plumose, mossy, dentiform, or other forms. Such are common among the native metals; as gold, silver, and copper. Mesolite is very frequently plumose. A “drusy crust” is the term applied to a thin rough layer of crystals, which invests either a large crystal or the surface of some other body lodged in the interior of cavities.

In the lamellar structure a development along the main axis would appear to have been checked, and the crystallographic force to have expended itself laterally; though this is not the invariable habit of a species under all circumstances, as exemplified by baryte. This structure consists of flat crystals, plates, or leaves. It is termed “tabular” when the plates are of uniform thickness, “lenticular” when they are thinner on the edges, “wedge-shaped” when sharp on one edge, “scaly” when the plates are thin and small, “foliaceous” when larger and easily separable; “micaceous” is also used to describe this kind of structure. It may also be curved lamellar and straight lamellar. Wollastonite, when flat lamellar, is called tabular spar; gypsum is frequently lenticular, talc scaly. Lamellar minerals when radiating from a centre often form fanshaped, wheel-like, almond-shaped, comb-like, and other groups.

In the granular structure, the force of crystallization nas been exerting itself along all the axes; but, from the multiplicity of crystallizing centres, there has been such mutual interference that no single individuals havo been able to assume perfect or even characteristic forms. The particles in a granular structure differ much in size. When coarse, the mineral is described as coarsely granular; when fine, finely granular; if not distinguishable by the naked eye, the structure is termed impalpable. Examples of the first may be observed in granular carbonate of lime, of the second in some varieties of specular iron, of the last in chalcedony, opal, and other species.

The above terms are indefinite, but of necessity, as there is every degree of fineness of structure in the mineral species, from perfectly impalpable, through all possible shades, to the coarsest granular. The term phanero-crystalline has been used for varieties in which the grains are distinct, and crypto-crystalline for those in which they are not discernible without the aid of a lens. Granular minerals, when easily crumbled in the fingers, are said to be friable.

The minute or crypto-crystalline minerals form aggregates somewhat similar to the above. When globular or oolitic, the minute crystals often appear to radiate from a centre, or form concentric crusts. These are often globular or nodular; as in dolomite. Somewhat similar are the stalactites and stalagmites, in which the mineral (especially rock-salt, calc-spar, malachite, haematite, limonite) has been deposited from a fluid dropping slowly from some overhanging body, or some rent in the roof of a cave. In this case there is generally found a long pendent cylinder or cone, the principal axis of which, generally hollow, is vertical, whilst the marginal parts are arranged at right angles to it, except where they curve round the termination of the tube, when they become hemispherical.

By far the largest masses of the mineral kingdom have, however, been produced under conditions in which a free development of their forms was excluded, and are termed amorphous. This has been the case with the greater portion of the minerals composing rocks or filling veins and dykes. The structure of these masses on the large scale belongs to geology, but some varieties of the textures, visible in hand specimens, may be noticed. The individual grains or masses have seldom any regular form, but appear round, long, or flat, according to circumstances, and as each has been more or less checked in the process of formation. Even then, however, a certain regularity in the position of the parts is often observable, as in graphic granite, where the axes of the skeleton crystals of quartz are parallel. The rock is termed massive when the grains which form it are small, or granular when they are longer and more distinct. Sometimes the rock becomes slaty, dividing into thin plates; or concretionary, forming roundish masses; at other times the interposition of some foreign substance (gas or vapour) has rendered it porous, cellular, or vesicular, giving rise to drusy cavities. These cavities are often empty, but have occasionally been more or less filled by products of change in the rock. It is named amygdaloidal when the cavities so filled have the form of an almond.

Changes of Crystalline Structure.

“Pseudomorphs” are minerals which appear under a form of crystallization which does not belong to the species. They may be recognized either by their having no cleavage, which is most usual, or by their cleavage being altogether different in direction from that of the mineral imitated. Generally they have rounded angles, rough and dull surfaces, and when broken show a granular structure. The faces of the crystal, moreover, are often covered with minute crystals of a form different from that of the mineral imitated, but which is that belonging to the substance now present. Occasionally the resemblance to real crystals is so perfect, from the perfect polish of the faces, that they are distinguished with difficulty. They may be frequently found still undergoing change.

Pseudomorphs have been classed under four heads

1. Pseudomorphs by Alteration.— Formed by a gradual change of composition in a species. Of these there are two varieties: they may be pseudomorphous by loss of an ingredient, or by addition of an ingredient; change of augite to steatite is an example of the first, and of galena into anglesite is one of the second.

2. Pseudomorphs by Substitution. —Those formed by the replacement of a mineral which has been removed, or is gradually undergoing removal; e.g., galena takes the form of pyromorphite.

3. Pseudomorphs by Incrustation.— Those formed through the incrustation of a crystal, which may be subsequently dissolved away. Often the cavity is afterwards filled by infiltration; e.g., change of fluor to quartz.

4. Pseudomorphs by Paramorphism.— Those formed when a mineral passes from one dimorphous state to another; e.g., change of aragonite to calcite.

These different kinds of change are not always distinguishable. In some cases a change may take place through alteration of the surface, and then, this process ceasing, the interior may be dissolved out, leaving a pseudomorph like one of incrustation; or a pseudomorph that appears to be a result of mere chemical alteration may be wholly due to substitution simply.

Again, changes of scapolite to a felspar, and of augite to uralite (hornblende), have been considered by Scheerer examples of paramorphism,—scapolite being considered dimorphous with some felspars, and augite with hornblende. But, while such paramorphic changes undoubtedly take place with aragonite, their occurrence in these silicates—which are common associates in the same rock, and must have been formed under like circumstances—is hardly probable.

Where mineral bodies have taken the form of organisms, it is more a case of molecular replacement than of true pseudomorphism.

Pseudomorphism should be understood, however, to consist, not simply in alteration of crystals, but in many instances of changes in beds of rock. Thus all serpentine, whether in mountain masses or in simple crystals, has been formed through a process of pseudomorphism—or, iu more general language, of metamorphism—of olivine and augite. The same is true of other magnesian rocks, as steatitic, talcose, and chlorite slates. The crystalline rocks often offer examples of a change similar in nature. The graphite of these rocks is probably but a metamorph of some vegetable organism. Thus the subject of metamorphism, as it bears on all crystalline rocks, and that of pseudomorphism, are but branches of one system of phenomena; the chemistry of both is the same, and a knowledge of such changes is indispensable to a study of the older rock strata of the earth.

The common change of pyrites, forming the main ingredient of the upper part of metallic lodes, to earthy red or brown iron ore, thus producing the “gossan” of miners, is one of many examples of these processes now in progress. Often the gossan contains disseminated silver or gold, derived from the decomposed ores. This is a case of pseudomorphism, as truly as when a simple crystal of pyrites becomes limonite; the mode of change and its laws are the same. Again, phosphates, vanadiates, and arsen ia tes of lead, &c., as well as carbonates and sulphates, are among the surface species, or those that occupy the upper part of metallic lodes; they are the results of alteration within those depths to which atmospheric agencies penetrate.

Pseudomorphs are always records of past existences, in some cases they may be the only evidence we possess of such prior existence. Figs. 238, 239 are pseudomorphs of quartz or hornstone after datholite; the measured angles of these crystals show that the imitated crystal was datholite; but that mineral does not now occur in crystals of either of these forms.

The process of petrification of organic bodies is in reality a species of pseudomorphic formation, and has been produced in all the above modes. External and internal casts of organic bodies are not uncommon. In other cases the original substance has been replaced by some mineral which has preserved, not merely the external form, but even the minutest detail of internal structure, —so that the different kinds of wood have been distinguished in their silicified trunks. The most common petrifying substances are silica and carbonate of lime. In encrinites, echinites, belemnites, and other fossils, the crystals of calc-spar often occur in very regular positions. In some varieties of petrified wood both the ligneous structure and the cleavage of the calc-spar are observable.

Different from the above are mineralized bodies, in which the original structure is still retained, but their chemical nature partially changed. In these a complete series may be often traced, as from 'wood or peat, through the varieties of brown coal, common coal, anthracite, and graphite.

Causes of Change.— The causes of change are the simplest and most universal operations about us :—(1) the process of gradual alteration to which some substances are liable on account of the presence of oxygen and carbonic acid in the atmosphere, and the reaction of substances thus formed on adjacent ingredients, aided or promoted by electrical currents or by heat; (2) the solvent power of ordinary waters, cold or hot, or of steam; (3) reactions, in accordance with chemical principles, of the ⅛gredients dissolved in these waters, or in mineral or sea waters, heated or at the ordinary temperature; (4) the action of gases exhaling from the earth; (5) changes referable to volcanic action.

Ordinary waters hold in solution, as is well known, more or less of mineral matter. When water containing carbonic acid is passed through a large number of ordinarily occurring minerals, it gives evidence of the presence of an alkali, or lime, or magnesia; and some of these minerals give the tests even with the first drops. Pure water gives with many of them a similar result, but more slowly. Limestone in forty-eight hours yields soluble ingredients to the extent of 0 - 4 to 1 per cent, of the whole mass. The lime, magnesia, and alkalies appear in the condition of carbonates; and the iron passes from the state of carbonate to that of peroxide during evaporation. The silicates of magnesia, lime, and manganese are especially ready in yielding to this action. Silica, however, is more soluble in ordinary than in carbonated water.

These facts illustrate two important points :—(1) that ordinary waters lying upon and filtering through the earth’s crust are constantly active in dissolving and decomposing minerals and rocks, and that even species reputed indestructible are thus acted upon; and (2) that the waters are thus furnishing themselves with agents capable of effecting other chemical changes. These waters penetrate all rocks, as well as percolate through soils. Hence the action is a universal one, everywhere going on; and the results are universal. Bones, shells, corals, and animal remains generally are also sources of carbonate of lime, phosphates, and fluorides; and plants may contribute also potash and soda, and sometimes silica.

Carbonic acid is a constant ingredient of the atmosphere, and is dissolved by the rains as they descend; hence this active decomposing agent is present in all ordinary waters; but it is also a result of different mineral changes. Sulphate of iron along with vegetable matters gives oxygen to the carbon of the vegetable matter, and thus produces carbonic acid and pyrites or sulphuret of iron; and the large quantities of pyrites in coal-beds show on how grand a scale this process has taken place. Sulphate of zinc in a similar manner produces carbonic acid and blende or sulphuret of zinc. Bischof observes that the carbonic acid which has thus been eliminated must have been sufficient in quantity to make an atmosphere of carbonic acid equal in height to our present atmosphere. Again, decomposition of sulphurets produces sulphuretted hydrogen; this by the oxidating action of the atmosphere forms sulphuric acid, and the sulphuric acid acting on limestone produces gypsum, and liberates carbonic acid. Sulphurous acid is also generated in the neighbourhood of volcanoes, and rapidly becomes sulphuric acid, with the same result. Moreover, silica in waters, if aided by heat, will decompose limestone and liberate carbonic acid. Hence it is that this gas is exceedingly common in exhalations from mineral springs; indeed it occurs more or less in all waters.

The dissolving and decomposing action of carbonated waters is therefore general. The sea also partakes of this character, and, in virtue of the numerous salts which it holds dissolved, is a powerful agent in carrying on the changes to which the process leads. Such changes and the various pseudomorphs to which they give rise have to be regarded as types and evidences of vast metamorphic transformations,—processes either of decay or of reformation which have modified widespread rock-masses,’and which are at the present time altering the structure of the crust of the earth. It is through a study of pseudomorphs, and of the processes which have gone to form them, that mineralogy is to become the germ from which alone the petrological department of geology can have its true development, and become a living instead of a merely speculative science.

Physical Properties of Minerals. Characters Depending on Light.

There are few more interesting departments of science than the relations of mineral bodies to light, and the modifications which it undergoes either when passing through them or when reflected from their surface. In this place, however, we only notice these phenomena so far as they point out distinctions in the internal constitution of minerals, or furnish characters for distinguishing one species from another.

Lustre.— Though the varieties of lustre admit of no precise or mathematical determination, they are of considerable value in mineralogy. One highly important distinction founded on them is that between minerals of metallic and non-metallic aspect or character. Transparency and opacity nearly coincide with this division,—the metallic minerals being almost constantly opaque, the non-metallic more or less transparent. Minerals which are perfectly opaque, and show the peculiar brilliancy and opacity of surface of polished metals, are named metallic; those which possess these properties in an inferior degree are semi-metallic; and those without these properties are non-metallic.

Lustre has reference to either the intensity or the quality of the reflected light, considered as distinct from colour. Several degrees in intensity have been named :—(1) splendent, when a mineral reflects light so perfectly as to be visible at a great distance, and lively and well-defined images are formed in its faces, as galena, specular iron, or cassiterite; (2) shining, when the reflected light is weak, and only forms indistinct and cloudy images, as heavy spar or calcite; (3) glistening, when the reflected light is so feeble as not to be observable at a greater distance than arm’s length, and no longer forms an image, as talc; (4) glimmering, when the mineral held near the eye in full clear daylight presents only a number of small shining points, as red haematite and granular limestone. When, as in chalk or kaolin, the lustre is so feeble as to be indiscernible, the mineral is said to be dull.

In regard to the kind or quality of the lustre, the following varieties are distinguished :—(1) the metallic, seen in much perfection in native metals and their compounds with sulphur, and imperfectly in glance coal; (2) adamantine, found in beautiful perfection in the diamond, and in some varieties of blende and cerussite; a modification is metallic adamantine, as seen in wolfram and black cerussite; (3) vitreous or glassy, seen in rock crystal, or common glass, or, inclining to adamantine, in flint glass; sub-vitreous is seen in broken calcite; (4) resinous, when the body appears as if smeared with oil, as in pitchstone, blende, and garnet; (5) waxy, like beeswax, as seen in wax-opal and ozocerite; (6) pearly, like mother-of-pearl, seen in gyrolite, talc, heulandite; (7) silky, the glimmering lustre seen on fine fibrous aggregates like amianthus, tremolite, chrysotile, krokidolite.

These degrees and kinds of lustre are generally exhibited differently by unlike faces of the same crystal, but always similarly by like faces. The lateral faces of a right square prism may thus differ in lustre from that of a terminal face. Thus the lustre of the lateral faces of apophyllite is vitreous, while that of the terminal, at right angles thereto, is pearly; chrysotile is silky when split along the fibres, dull when at right angles to them.

The surface of a cleavage plane, in foliated minerals, generally differs in lustre from the sides; and here again in some cases the latter are vitreous, while the former is pearly, as in heulandite.

As shown by Haidinger, only the vitreous, adamantine, and metallic lustres belong to faces perfectly smooth and pure. In the first, the index of refraction of the mineral is 1 ‘3 to 1 *8; in the second, Γ9 to 2 ’ 5; in the third, above 2 - 5. The pearly lustre is a result of reflexion from numberless lamellae, or cleavage planes, within a translucent mineral; and in hydrated minerals, as in the zeolites, it is the result of incipient change,—namely, a loss of water which ensues upon exposure to the atmosphere.

Colour.— This is a property which is of very inferior value. Minerals are so seldom, if ever, absolutely pure that very minute quantities of an intensely coloured impurity may impart colour to a substance inherently colourless, or overpower a feebler colour which may be its own.

Some few minerals have colour so strong, or have a constitution so little susceptible of intermixture, that they retain almost unimpaired the colour special to them. Such a substance is pyrite; its brass-yellow colour maybe heightened to gold-yellow by intermixture with copper sulphide, or it may be slightly bleached by arsenic; but the nature of its composition does not admit of the intrusion of ordinary colouring ingredients. The yellow of native gold, again, may be paled by impoverishment with the white of silver, down to the dull tint of electrum; but no foreign colouring matter can intrude itself into a metallic mass. Such substances as these,—native metals, sulphides, and oxides,—have colours essential to them, dependent on their constitution, and to a great extent characteristic of the species.

A second class of minerals are colourless of themselves, and thus very subject to the influence of minute quantities of foreign tinctorial impurity. These are absolutely transparent and devoid of colour when in crystals, but white and opaque when reduced to powder; as ice and snow, calcite and chalk, rock-crystal and sand. But such substances are generally coloured; “muddied” it would be called in the first case, though it is equally so with the others. Such false colour may be imparted in several ways. It may be (1) from their holding dissolved some colouring matter; (2) from mechanical mixture of colouring substances such as metallic oxides, or minute crystals (“endomorphs”) of another mineral; or (3) from chemical replacement,—the substitution of a smaller or larger quantity of a coloured isomorphous ingredient.

As illustration of the first, silica, colourless in rock-crystal, has been found of almost every tint, due frequently to volatile hydrocarbons which are dissipated by heat. Fluorite also, found of almost every shade of every colour, may possibly be to a certain extent referred here.

Quartz, felspar, and calcite are often coloured accidentally by imbedded layers of foreign “inclusions,” or by “spangling endomorphs.” These are mechanically mixed, so far as regards their presence in a structure of different and non-assimilable chemical composition, but crystallographically arranged. They either mark the lines of interrupted or intermittent growth; or, in the case of endomorphs, the axial positions of the minute intruding foreign crystals lie in one plane, or in the same sets of planes.

As an instance of colours introduced through definite chemical replacement, calcite may be cited. Carbonate of lime is colourless; if a portion of this be replaced by carbonate of magnesia there is a certain amount of pearly opacity; if by carbonate of manganese, of a pink tinge; if by carbonate of iron, of yellow, which may be increased through oxygen absorption and “weathering” to an ochre tint, and ultimately to a dark brown.

Sulphuret of zinc, chemically white, and mineralogically transparent, may, through metallic substitution, be found of almost all tints of yellow, orange, brown, and black. Again, hornblende, augite, and garnet,—silicates, which in their purest states of tremolite, malacolite, and water garnet are colourless,—acquire green, brown, red, and black tints from the assimilation of other metallic silicates.

Hence it would appear that a very advanced practical knowledge of the subject is necessary to enable us to avail ourselves of the information which is to be derived from this external feature.

The accidentally coloured minerals sometimes present two or more colours or tints, even in a single crystal,—very remarkable examples occurring in fluor-spar, apatite, sapphire, amethyst, tourmaline, and cyanite. This is still more common in compound minerals, on which the colours are variously arranged in points, streaks, clouds, veins, stripes, bands, or in brecciated and ruin-like forms. Some minerals again change their colour from exposure to light, the air, or damp. Then either the surface alone is affected or “tarnished,” and appears covered as with a thin film, producing in some minerals, as silver and arsenic, only one colour; in others, as chalcopyrite, haematite, bismuth, stibine, and anthracite, various or iridescent hues, when they are said to have a pavonine lustre. Or occasionally the change pervades the whole mineral, the colour either becoming paler, or disappearing, as in chrysoprase and rose-quartz, or becoming darker, as in brown spar, siderite, and rhodonite. In a few minerals a complete change of colour takes place, as in heterosite, and in the chlorophaeite of the Western Isles of Scotland, which, on exposure for a few’ hours, passes from a transparent yellow-green to black. These mutations are generally connected with some chemical or physical change. The tarnished colours sometimes only appear on certain faces of a crystal belonging to a peculiar form. Thus a crystal of copper pyrites (like fig. 89) has one face P' free from tarnish; the faces b and c, close to P z , dark blue; the remainder of c, first violet, and then, close to P, gold-yellow'.

Some crystalline minerals exhibit in certain directions a very lively play or change of colours from reflected light. It is well seen in many various hues on the cleavage-planes of labradorite, and seems produced by a multitude of very thin quadrangular pores, interposed in the mineral, like minute parallel laminae. On the cleavage-plane > of hypersthene it appears copper-red, and is occasioned by similar pores, or by numerous small brown or black laminae of some foreign substance interposed in a parallel position between the planes of the hypersthene. The chatoyant or changing colours of the sun-stone arise from scales of haematite similarly interposed, and that of avanturine from scales of mica. The play of colour in the noble opal seems to be produced very nearly in the same manner as that in the labradorite. A similar opalescence is seen in certain minerals when cut in particular forms. In the sapphire, cut hemispherically over the chief axis, it appears like a star with six rays; in garnet it shows four rays; in certain varieties of chrysoberyl and of adularia it has a bluish tint; and it is also very remarkable in the cat’s-eye variety of quartz. Iridescence often arises from very fine fissures, producing semicircular arches of prismatic tints, which, like the colours of thin plates in general, are referred to the interference of light.

Streak.— This name is applied to the appearance and the colour of the line or furrow produced in minerals by drawing the edge of a hard-tempered knife or file along their surface, or to the stain obtained by rubbing a soft mineral on such a substance as paper or porcelain. Taken along with the hardness, which may to a certain extent be determined by the same operation, it is one of the most valuable tests which we possess.

The furrow mav be lustrous or it may be dull. Powder or splinters may lie along its course, or a still adherent ridge may have been merely rolled over. The furrow and the powder may each be possessed of colour, though such may not be distinguishable in the mineral, or may have a colour quite different from that of the mineral. Three illustrations of the usefulness of this test may suffice. Argentiferous gold, chalcopyrite, and pyrite, differing immensely in value, may readily be mistaken for each other. The knife, when drawn along the surface of the first, sticks in it, ruts up an adhering ridge, and leaves a shining streak of the same colour as the specimen. When drawn along the second it ruts up a trench covered with a dusty powder, which when rubbed on paper or in the hand is greenish yellow. When drawn along the third it has no effect, as pyrite is harder than the knife. Psilomelane, haematite, and limonite all occur in black, glossy, stalactitic forms, and have all been termed “black haematite.” There is here also great difference in the value. The knife makes little impression on psilomelane, but leaves a blue lustrous line; it makes a blood-red line in haematite, and a rich ochre-yellow in limonite. Graphite and molybdenite both crystallize in hexagonal plates, both occur in the same rocks, both have a gι ’ ey-black colour and a brilliant metallic lustre, both stain the hands or paper; the streak of the first—best seen on paper—is black, tending to blue; that of the last is greenish. Rough porcelain is the best material for determining the streak of soft minerals.

Diaphaneity.— Minerals, and even different specimens of the same species, vary much in this quality. Some transmit so much light that small objects can be clearly seen, or letters read, when placed behind them; such are named transparent. They are semitransparent when the object is seen only dimly, as through a cloud, and translucent when the light that passes through is so broken that the form of the object can be no longer discerned; some minerals are only thus translucent on the thinnest edges. Others transmit no light, and are named opaque.

Refraction.— It has already been mentioned that most crystals—all, in fact, except those of the cubical system— exhibit the phenomena of double refraction. For a general explanation of these phenomena the reader is referred to Light, vol. xv. p. 609 sq.

The direction in which there is no double refraction is named the optic axis of the crystal,—sometimes, less happily, the axis of double refraction. Now in certain minerals it is found that there is only one direction with this property, whereas in other’s there are two such directions; and they have in consequence been divided into uniaxal and binaxal. To the former belong all crystals of the tetragonal and hexagonal systems, to the latter all those of the other three systems. In the former the optic axis coincides with or is parallel to the crystallographic chief axis. In some uniaxal crystals the index of refraction for the extraordinary ray is greater than for the ordinary ray; and in others it is smaller. According as it is greater or less they are said to have positive (attractive) or negative (repulsive) double refraction.

Quartz is an example of the former, the index of refraction, according to Malus, being for 0 = 1’5484, for E=1’5582; calc-spar of the latter, the index of 0 being =1’6543, that of E 1’4833. The index of E is in both cases taken at its maximum.

It should be observed that the optic axes are not single lines, but directions parallel to a line, passing through every part of the crystal. It is also important to remark that this property divides crystals into three precise groups :—the cubic, with single refraction; the tetragonal and hexagonal, with double refraction, and uniaxal; those of the other three systems, also double, but binaxal. These properties are therefore of the greatest use in determining the system to which a mineral belongs.

Polarization.— Intimately connected with this property is that of the polarization of light, which affords an easier means of determining mineralogical characteristics than the direct study of double refraction. For the elements of this subject see Light, vol. xv. p. 611 sq.

While a consideration of the optic axes enabled us merely to arrange the systems of crystallization in three groups, the phenomena of polarization not only bear out a further subdivision of the whole into the above six systems, but disclose, in many cases, phenomena markedly special to individual species. The optical consideration of these phenomena enables us to fix three directions at right angles to one another—called the axes of optical elasticity—such that the effect of the crystal on the luminous vibrations of the elastic ether is a maximum in one of these directions, a minimum in a second, and a maximum-minimum in the third. The length of these axes is chosen in terms of this action. In certain cases the direction of the axes of optical elasticity is different for light of different colours.

The position of these axes in relation to the crystallographic axes, and the ratios of their lengths, enable us to class all crystals as follows:—

1. Crystals of the cubic system. Here the three axes of elasticity are all equal. The refraction is simple.

2. Crystals of the tetragonal and of the rhombohedral systems. Two of the axes of optical elasticity are equal in these systems; the third is greater or less according as the crystals are negative or positive. The two equal axes lie in a plane perpendicular to the principal crystallographic axes; the third axis coincides with the principal axis.

3. Crystals of the right prismatic system. The direction of the three axes of optical elasticity coincides with the crystallographic axes, taken parallel to the diagonals of the base of the rhombohedron, and to the vertical edge of the prism (the primitive parallelepiped of Levy).

4. Crystals of the oblique prismatic system. Only one of the axes of optical elasticity coincides necessarily with the crystallographical horizontal axis, or the diagonally horizontal axis of the rhombic base, the direction of the two others not having any evident relation, a priori, with the inclined or diagonally inclined axis of the base, and with the vertical axis (or vertical edge of the primitive parallelepiped).

5. Crystals of the anorthic system. The three axes of optical elasticity have no relation that can be assigned a priori to the crystallographic axes, whatever position may be assigned to these in relation to the primitive solid.

In crystals belonging to the last three systems the three axes of elasticity are unequal.

The axes of elasticity are in general such that a ray passing through the crystal in the direction of any one of them is divided into two, which follow that direction with different velocities depending on the lengths of the other two axes. To any other direction there will in general also correspond two different velocities; but their ratio will now depend in a more complex manner on all three axes. In two directions (and only in two, if the axes are all unequal) the ratio becomes unity, or the ray is not divided. These directions are the optic axes.

The displacement of the axes of elasticity for light of different colours, already mentioned, takes place for two axes in crystals of the oblique prismatic system and for all three axes in the anorthic {i,e., doubly oblique) system. In the other systems it does not occur.

In order to follow the distinctive features of the different systems farther, it is necessary to consider the colour phenomena which they display, when examined in a beam of polarized light. Various instruments have been devised for this purpose, as, e.g., the polarizing apparatus of Norrenberg, fitted with a condensing lens below and above the crystal slice, or with a low-power (3-inch) eye-piece. The polariscope of Hoffman of Paris is more efficient, but the apparatus of Descloizeaux (fig. 240), who has made this mode of investigation a special study, has the widest scope of usefulness. In this apparatus a blackened mirror is employed for polarizing the light, taking the place of a tourmaline plate, a Nicol’s prism, or a bundle of thin glass. The mirror is inferior to the other two in completeness of polarizing power, and in not admitting of rotation; while it shares this defect with the last. It is, however, superior to all in extent of field, while it does not, like the first, affect white light. A Nicol’s prism is used for examining or analysing the light which passes.

The description of the many beautiful phenomena that may be observed witn polarizing apparatus when applied to sections of crvstak belongs to the subject of Optics (Physical), to which heading also we must refer for the phenomena of circular polarization.

Double Refraction and Polarization of Composite Crystals.— In all the crystallized bodies whose action upon light we have been considering, the phenomena are identical in all parallel directions, the smallest fragment having the same property as the largest, from whatever part of the crystal it is taken. In the mineral world, however (and among the products of artificial crystallization), there occur crystals which are composed of several individual crystals whose axes are not parallel. These crystals sometimes occur in such regular symmetrical forms that mineralogists have long regarded them as simple forms; and it is probable that they would have still been so viewed if they had not been exposed to the scrutiny of polarized light.

A composite structure has been observed in the case of Brazilian topaz, sulphate of potash, and apophyllite. Bipyramidal sulphate of potash, which Count Bournon supposed to be a simple crystal, was found to be a tesselated crystal, composed of three pairs of crystals of the prismatic sulphate of potash combined so that each pair had their principal axes parallel. When exposed to polarized light, each pair gave the system of binaxal rings, and when held at a distance from the eye had the tesselated appearance shown in fig. 241, each opposite pair of the triangles having the same tint.

The most remarkable of this class of minerals is the tesselated apophyllite. The examination of this body by polarized light is due to Brewster. F or his results the reader is referred to his paper in the Edinburgh Transactions, vol. ix. p. 323.

Figs. 242, 243 are representations of the figure produced in polarized light by an internal slice of the barrel or cylindrical apophyllite from Kudlisaet, in Disco Island. The figures are from different specimens. The shaded part of them has only one axis of double refraction, while the four sectors have two axes. The mechanical structure of the cleavage planes resembles the optical figure even after the planes are ground.

The minerals stilbite, heulandite, chabasite, and many others, are similarly complex in structure.

Crystals with Planes of Double Refraction.— Analcime, a mineral ranked among the cubical crystals, was found by Brewster to be singular in its action upon light, and to exhibit the extraordinary property .of many planes of double refraction, or planes to which the double-refracting structure was related in the same manner as it is to one or two axes in other minerals. It crystallizes most commonly in the form of the icositetrahedron. If we suppose a complete crystal of it to be exposed to polarized light, it will give the remarkable figure shown in fig. 244, where the dark shaded lines represent planes in which there is neither double refraction nor polarization,—the double refraction and the tints commencing at these planes, and reaching their maximum in the centre of the space enclosed by three of the dark lines. When light is transmitted through any pair of the four planes which are adjacent to any of the three axes of the solid, it is doubly refracted, the least refracted image being the extraordinary one, and consequently the double refraction negative in relation to the axes to which the doubly-refracted ray is perpendicular. If we suppose the crystal to have the form of a cube, the planes of double refraction will be, as in fig. 245, a plane passing through the two diagonals of each face of the cube.

The tints vary as the square of the distance from the nearest plane of double refraction.

Pleochroism.— Closely connected with double refraction is that property of transparent minerals named pleochroism (of many colours), in consequence of which they exhibit distinct colours when viewed by transmitted light in different directions. Crystals of the cubic system do not show this property, whilst in those of the other systems it appears in more or less perfection,—in tetragonal and hexagonal minerals as dichroism (two colours), in the rhombic and clinic systems as trichroism (three colours). In most cases these changes of colour are not very decided, and appear rather as different tints or shades than as distinct colours. The most remarkable of dichromatic minerals are the magnesian mica from Vesuvius, the tourmaline, and ripidolite; of trichromatic, iolite, andalusite from Brazil, diaspore from Schemnitz, and axinite.

In a specimen of yellow Iceland spar the extraordinary image is of an orange-yellow colour, while the ordinary image is yellowish white. Along the axis of double refraction the colour of the two pencils is exactly the same, and the difference of colour increases with the inclination of the refracted ray to the axis. This is the invariable law of the phenomena in uniaxal crystals. Sir John Herschel found several tourmalines to have a blood-red colour along the axis, and at right angles to it to be yellow-green. There can be little doubt that this property will be found in every crystal of sufficient refraction. Even if the crystal is colourless, a slight inequality in the intensity of the two images may be observed; and when it is distinctly coloured the difference of intensity is very easily seen, even when the two colours are not of a different kind.

The phenomena of dichroism are best seen in crystals with two axes of double refraction, and are well exemplified in iolite, a mineral which crystallizes in six-or twelve-sided prisms. These prisms are of a deep blue colour when seen along the axis, and of a yellowish brown colour when viewed in a direction perpendicular to it.

If abed (fig. 246) is a section of the prism of iolite in a plane parallel to the axis of the prism, the transmitted light will be blue through the faces ab and de, and yellowish brown through ad, be, and in every direction perpendicular to the axis of the prism. If we grind down the angles a, c, b, d, so as to replace them with faces mn, m ’ n' and op, o'p', inclined 31° 41' to ad, or to the axis of the prism, then, if the plane abed passes through the optic axes, we shall observe, by transmitting polarized light through the crystal in the directions ac, bd, and subsequently analysing it, a system of rings round each of these axes. The system will exhibit the individual rings very plainly if the crystal is thin; but if it is thick, we shall observe, when the plane abed is perpendicular to the plane of primitive polarization, some branches of blue and white light diverging in the form of a cross from the centre of the system of rings, or the poles of no polarization, as shown at p and p' (fig. 247), where the shaded branches represent the blue ones. The summits of the blue masses are tipped with purple, and are separated by whitish light in some specimens and yellowish light in others. The white light becomes more blue from p and p' to o, where it is quite blue, and more yellow from p and p' to c and d, where it is completely yellow. When the plane abed is in the plane of primitive polarization, the poles p, p' are marked by spots of white light, but everywhere else the light is a deep blue.

In the plane cadb (fig. 247) the mineral, when we look through it by common light, exhibits no other colour but yellow, mixed with a small quantity of blue, polarized in an opposite plane. The ordinary image at c and d is yellowish brown, and the extraordinary image faint blue, the former receiving some blue rays and the latter some yellow ones from c and d to a and b, where the difference of colour is still well-marked. The yellow image becomes fainter from α and b to p and p', till it changes into blue, and the faint blue image is strengthened by other blue rays, till the intensity of the two blue images is nearly equal. As the incident ray advances from c and d to p and p', the faint blue image becomes more intense, and the yellow one, receiving an accession of blue rays, becomes of a bluish white colour. The ordinary image is whitish from p and p' to o, and the extraordinary is deep blue; but the whiteness gradually diminishes towards o, when they are both almost equally blue.

The principal axis of double refraction in iolite is negative. The most refracted image is purplish blue, and the least refracted one yellowish brown.

Brewster found that the dichroism of several crystals is changed by heat, and that in some cases this property may be communicated to them. Babinet found that all negative crystals, such as calcareous spar, corundum (including ruby and sapphire), tourmaline, and emerald, absorb in a greater degree the ordinary ray, with the exception of beryl, apatite, and some apophyllites; while positive crystals, such as zircon, smoky quartz, sulphate of lime, and common apophyllite, absorb in a greater degree the extraordinary ray. Babinet found also that certain crystals, such as red tourmaline and ruby, transmit rays of their peculiar colour without being polarized,—in which cases the black cross of their system of rings is coloured, and this unpolarized light exists both in the ordinary and extraordinary ray.

Haidιnger devised an instrument for showing and for testing the pleochroism of minerals. In fig. 248, p is an oblong cleavage-rhombohedron of Iceland spar which has two glass prisms w,vj of

18° cemented to its ends with Canada balsam. This combination is placed in a metallic case, which has a convex lens I at one end and a square hole o about the fifteenth of an inch in width at the other. The lens is of a focal distance which shows an object held about half an inch from the square hole.

On looking through the lens and prisms two images of the square hole are seen just touching each other. The light of the one image is polarized in the plane which intersects the short diagonal of the prism; that of the other is polarized in the plane of the longer diagonal. When a pleochroic crystal or fragment is held at focal distance and examined by transmitted light, then, on the turning of the instrument bringing the polarization of its planes into coincidence with those of the crystal, the two images of the square opening will show the colours of the oppositely polarized pencils of which the light transmitted by the crystal is composed; this constitutes its pleochroism. The dichroism is then seen by looking through the crystal in one direction only, and the contrast of the two colours is made more obvious.

Phosphorescence.— This is the property possessed by particular minerals of emitting light in certain circumstances, without combustion or ignition.

Thus some minerals appear luminous when taken into the dark, after being for a time exposed to the sun’s rays or even to the ordinary daylight. Many diamonds, and also calcined barytes, exhibit this property in a remarkable degree; less so aragonite, calc-spar, and chalk. Many minerals, including the greater part of those thus rendered phosphorescent by the influence of the sun, also become so through heat. Thus some topazes, diamonds, and varieties of fluor-spar become luminous by the heat of the hand; other varieties of fluor-spar, and phosphorite, require a temperature near that of boiling water; whilst calc-spar and many silicates are only phosphorescent at from 400° to 700° Fahr.

Electricity produces phosphorescence in some minerals, as in green fluor-spar and calcined barytes. In others it is excited when they are struck, rubbed, split, or broken; as in many varieties of zinc-blende and dolomite when scratched with a quill, pieces of quartz when rubbed on each other, and plates of mica or needles of pectolite when suddenly separated.

The light emitted by phosphorescent minerals is of various tints. The variety of fluor called chlorophane emits, as its name expresses, a green light. The same particle may emit varying tints, as in the fluor from Aberdeenshire, which, as the heat falls, or the energy of the phosphorescence wanes, emits tints which pass from violet, through blue, green, and yellow, to dull purplish red. The yellow blende from the same place is vividly phosphorescent when heated. Fluor generally phosphoresces with a tint of its own colour.

Too high a heat destroys the phosphorescence, which may, however, be restored by either exposure to sun’s light or w electricity.

The mineral phosphoresces vividly when the discharge passes through it; it generally phosphoresces with a different colour after it has been thus recharged.

Fluorescence, is the property whereby rays of light of a refrangibility higher than those ordinarily seen by the human eye are rendered visible. The substance when placed in the violet end of the spectrum, and carried beyond it into the invisible rays, becomes luminous, through “degrading” the rays of extreme refrangibility. This property is well marked in those varieties of fluorite which are pale green by transmitted light, and deep purple by reflected light. Ozocerite and some petroleums also exhibit the property.

Electric, Magnetic, and Thermic Properties. Electricity.— Friction, pressure, and heat may all excite electricity in minerals. To observe this property delicate electroscopes are required, formed of a light needle terminating at both ends in small balls, and suspended horizontally on a steel pivot by an agate cup. Such an instrument, can be electrified negatively by touching it with a stick of sealing-wax excited by rubbing, or positively by merely bringing the wax so near as to attract the needle. When the instrument is in this state, the mineral, if also rendered electric by heat or friction, will attract or repel the needle according as it has acquired electricity of an opposite or of a similar kind; but if the mineral is not electric it will attract the needle in both conditions alike.

Most precious stones become electric from friction, and are either positive or negative according as their surface is smooth or rough. All gems become positive when polished; the diamond even when unpolished is positive. Pressure between the fingers will excite distinct positive electricity in pieces of transparent double-refracting calc-spar. Topaz, aragonite, fluor-spar, carbonate of lead, quartz, and other minerals show this property, but in a much smaller degree. Some bodies remain excited much longer than others, topaz for a very long time. Heat or change of temperature excites electricity in many crystals; as in tourmaline, calamine, topaz, calcspar, beryl, barytes, fluor-spar, diamond, garnet, and others; these are hence said to be thermo-or pyro-electric. Some acquire polar pyro-electricity, or the two electricities appear in opposite parts of the crystal, which are named its electric poles. Each pole is alternately positive and negative, the one when the mineral is heating, the other when it is cooling. HankeΓs investigations of these phenomena are specially noteworthy.

As already noticed, many polar electric minerals are also remarkable for their hemimorphic crystal forms. Tourmaline, calamine, and boracite are among the species thus affected. The polarity continues so long as the temperature is increasing, and becomes reversed when it commences to decline; and when the heat is stationary it disappears.

Kose and Reiss name one of the poles the analogue electric pole, and the other the antilogue electric pole. The former becomes positive while the crystal is heating, and negative while cooling; the latter negative while heating, and positive while cooling. Becquerel found that in tourmaline at 30° C. electrical polarity was sensible; it continued unchanged to 150°, as long as the temperature continued to rise; if the temperature remained stationary an instant, the polarity disappeared, but shortly manifested itself reversed, when the temperature commenced to decline. If but one end of the crystal was heated the crystal was unpolarized, and when two sides were unequally heated each acquired an electrical state independent of the other. In tourmaline the extremities of the prism are dissimilarly modified, and that end which presents the greater number of planes is the antilogue pole; or, if the number of planes is the same, the secondary rhombohedrons of the antilogue pole have (one or more of them) longer vertical axes than those of the analogue pole. Fig. 249 (tourmaline) is the antilogue pole (negative under increasing heat), and fig. 250 the analogue pole. The pyramid of the analogue end is more flattened by its facets than that of the antilogue end; thus e s and d⅛ of the antilogue end are more acuminating than e 1 and cP of the analogue end. The same is the case with the other two crystals (figs. 251, 252).

Pyro-electricity has been observed in the following substances: — tourmaline, topaz, axinite, boracite, scolezite, prehnite, electric calamine, sphene, rhodizite, heavy spar, rock-crystal.

Pyro-electricity is of two kinds,—either terminally polar or centrally polar. In the former the extremities are opposite poles. In the latter two sides of a prism are of the same name, and the opposite pole to each is intermediate between the two.

The examples of the first kind are tourmaline, calamine, and scolezite, which are uniaxal; axinite, binaxal; boracite and rhodizite, with four axes. Calamine, like tourmaline, has the sharper extremity the antilogue end, and the more flattened the analogue. Compound crystals from Altenberg have both ends analogue, and the portion which lies between the twins antilogue electric; the pyro-electric axis corresponds with the vertical axis of the prism, as in tourmaline. Boracite, which crystallizes in cubic forms, with the opposite solid angles differently modified, has four pyro-electric axes, corresponding to the four octahedral axes. In fig. 253 of this species, the plane which has its angles modified by V is the antilogue pole, and that with the unmodified angles the analogue pole; and, generally, the antilogue pole has either more numerous or larger facets. Rhodizite resembles boracite in its pyro-electricity.

The species in which pyro-electricity of the second kind has been observed are prehnite and topaz. If fig. 254 represent a tabular crystal of prehnite, the poles will be situated as marked, the analogue being central, and the antilogue at either extremity of the shorter diagonal of the rhombic prism. Topaz has in a similar manner a central analogue pole, and an antilogue at either extremity of the shorter diagonal. In some instances there is a separate Set of similar poles near one or the other angle, as in fig. 255; this must be due to the crystals being of a composite nature.

Magnetism.— This property is very characteristic of the few minerals in which it occurs,—chiefly ores of iron or nickel. Some magnetic iron ores possess polar magnetism, or are natural magnets; while the common varieties of magnetite, meteoric iron, magnetic pyrites, precious garnet, and other minerals, are simply magnetic. Most minerals are only attracted by the magnet, but do not themselves attract iron.

Minerals, as other substances, have also been divided into magnetic and diamagnetic. See Magnetism.

The ordinary mode of testing whether a mineral is magnetic or not is to bring it near a pole of a delicately suspended magnetic needle, and observe whether it causes it to vibrate. Another mode is to apply a strong magnet to the mineral in powder. These are sufficient for the mineralogist. Delesse has experimented extensively upon the magnetic force of minerals, and has determined the relative amount for numerous species. Calling this force for Styrian steel 100, the following are some of his results: — [table]

Crystallomagnetic Action.— The magnetic polarity thus far alluded to belongs to the mass, and has no relation to crystalline form. There is also a kind of polarity directly related to the crystalline or optic axes of minerals. A crystal of cyanite, suspended horizontally, points to the north, by the magnetic power of the earth only, and is a true compass needle, from which even the declination may be obtained; and the line of direction is the line of the optic axes. Other crystals, which are called negative, take a transverse or equatorial position. The latter are diamagnetic crystals.

Conductivity for Heat.— Senarmont found that the conducting power of colloids and of crystals of the cubic system is equal in all directions, but that it varies in different directions in crystals belonging to all the other systems, exhibiting characters analogous to those deduced from their double refraction, conformable with the optic axes of the crystal, and referable, as in the latter case, to axes of elasticity, or unequal compression of the molecules.

The fundamental fact is easily shown by taking two slices of rock-crystal, one cut transverse to the axis and one parallel to it. Through the centre of each plate a small hole is drilled for the reception of a bent wire, which by insertion into the hole sustains the plate. The other end of the wire is to be heated, and the rate of the conduction of the heat is rendered visible by the amount of a thin coating of beeswax, with which the plate has been previously coated, which is melted round the central hole. It will be seen that in the transverse slice the wax is melted in a circular form, while in the longitudinal slice the form is elliptical (fig. 256). The conduction is equal in all directions, as regards the transverse axes of the hexagonal {>rism, but more rapid in one direction in the ougitudinal slice, and that direction is the line of its optic axis. In the case of quartz the two diameters of the ellipse are as 1000 to 1312.

If the regular disposition of the molecules of amorphous bodies be interfered with by unequal tension or compression, the regularity of their power of conducting heat is destroyed, and they also show elliptical forms of melted wax; and the shorter axis of the ellipse is in the line of Pressure or undue packing of the molecules.

he heat thus does not travel so fast in this direction,—partly because it is spent in the heating up of the greater number of molecules. Hence we might conclude that along the main axis of quartz a smaller number of molecules are packed in an equal space than along the transverse. The following are the more important of Senarmont’s results.

1. Crystals of the tetragonal and rhombohedral systems have one axis of conductivity which is either greater or smaller than the others, and this axis coincides with the main crystallographic axis. The isothermal surfaces are ellipses which lie in the line of this axis, and these ellipses may be either elongated or flattened in the direction of this line.

2. In crystals of the right prismatic system the isothermal surfaces have three unequal axes, which coincide with crystallographic axes drawn parallel to the edges of the rectangular prism.

3. In crystals of the oblique rhombic system the isothermal surfaces have three unequal axes, one of which coincides with the horizontal diagonal of the base, while the other two have directions which are not referable to any law.

4. In crystals of the anorthic system the isothermal surfaces have three unequal axes, all with indeterminable positions.

In crystals of a single axis there appears to exist no constant relation between the axis of optic elasticity, whether maximum or minimum, and the axis of the greatest or of the least calorific conductibility. Thus, of the minerals examined by Senarmont, quartz ( + ), calcite ( - ), cassiterite ( + ), rutile ( + ), and calomel ( + ) have all their greatest axis of conductibility parallel to the principal axis; idocrase, beryl, tourmaline, and corundum, all optically negative, have on the contrary their smallest axis of conductibility parallel to the axis.

In crystals belonging to the oblique rhombic system there is rarely coincidence between the thermic axes and the axes of optic elasticity. In gypsum and in felspar these lie apart to a marked extent.

Dilatation by Heat.— In crystals of those systems in which the molecules are arranged unequally as regards their axes, the amount of their dilatation when heated is unequal in the direction of their axes. Our knowledge of this subject is chiefly due to Mitscherlich.

In crystals of cubic symmetry the expansion is equal in all directions. The dimetric systems—the pyramidal and hexagonal— are brought together as regards this quality, inasmuch as the axes of volumetric change are in these the same; for, while these in the pyramidal correspond with the crystallographic axes, in the hexagonal the three axes are the vertical, one lateral axis, and an axis lying intermediate to the other two and at right angles to the first lateral axis. The expansion along the principal axis may be either greater or less than along the others; and in some minerals there is even contraction along one axis.

In the right prismatic system the axes of dilatation correspond to those of form. In the oblique prismatic one axis corresponds with the orthodiagonal, but the others make angles not only with the other crystallographic axes but, strange to say, with the axes both of thermic conductivity and of optic elasticity. We are as yet ignorant of the properties of anorthic crystals in this respect.

As a consequence of this unequal expansion along different axes, the angles of crystals, other than those of the cubic system, are altered under the influence of heat. The alteration is extreme in the case of calcite, where, through elongation along the vertical axis, with some concomitant contraction of the transverse, the angle of the rhombohedric faces is, when the crystal is heated from 32° to 212° F., diminished from 105° 5'to 104° 56' 23",— the form thus approaching that of a cube, as the temperature is raised.

Dolomite, in the same range of temperature, diminishes 4' 46". In some rhombohedrons, as of calc-spar, the vertical axis is lengthened (and the lateral shortened), while in others, like quartz, the reverse is true. The variation is such, either way, that the double refraction is diminished with the increase of heat; for calc-spar possesses negative double refraction, and quartz positive. According to Fresnel the same is true of gypsum. The dilatation for calc-spar, according to experiment, is 0*001961.

Kopp has shown that in the carbonates of lime, magnesia, iron, manganese, and zinc, which are nearly the same in the angle of their crystals, the vertical axis is shorter the greater the atomic volume And since heat diminishes the density, and therefore necessarily increases the volume, the axis a should be lengthened by an increase of temperature, as is actually the case. He has determined by calculation that the change of angle from 32° to 212° should be 7' 37".

Although in the greater number of cases the variations are so small as to be scarcely measurable, yet they may be sufficient for establishing a difference between substances which have identical geometric form while belonging to different systems of crystallization. The angle of a rhombohedron might at a certain temperature be 90°, and so coincide with a cube; but that angle would in a rhombohedron change whenever the temperature altered, while the angle of a true monometric cube is constant at all temperatures. The increase in volume and diminution in density which generally result from heating are always accompanied by a change in optical properties. In trimetric crystals, where the principal indices alter unequally, the change affects the amount of divergence of the optic axes. The amount of alteration in gypsum, when the divergence is diminished, is extreme. At the ordinary temperature the angle of the divergence of thé optic axes which lie in the plane of symmetry is about 90° for red light; when heated to 177° it is diminished to 0°, and for the moment the crystal appears to be uniaxal. When more highly heated, the axes again diverge, but in a plane at right angles to the original one, and in cooling these changes take place in reverse order. In barytes and celestine again, the alteration in the angle of the optic axes is a divergence when heated.

Characters depending on Cohesion.

These characters are of five kinds:—(1) hardness,.(2) tenacity, (3) elasticity, (4) cleavage, (5) fracture. All may be considered as related to the power of resisting attempts to separate one part from another.

1. Hardness.— A harder body is distinguished from a softer, either by attempting to scratch the one with the other, or by trying each with a file. Each of these methods is used by the mineralogist in determining the hardness of the species, though the latter is in most cases to be preferred. Both methods should be employed when practicable.

Certain varieties of some minerals give a low hardness under the file, owing either to impurities or imperfect aggregation of the particles, while they scratch another mineral upon which a file would have no effect, showing that the particles of the first are hard, though loosely aggregated. Chiastolite, spinel, and sapphire are common examples of this. When the mineral is too hard to be impressed by a file, the peculiarity of the grating sound will suffice for the practised ear.

Mohs introduced a scale of hardness, consisting of ten minerals, which gradually increase in hardness from 1 to 10. The intervals between 2 and 3 and 5 and 6 are larger than the others. Breithaupt has therefore introduced another degree of hardness between each of the above, and thus his scale consists of twelve minerals.

The scale is as follows [table]

If the file abrades the mineral under trial with the same ease as No. 4, and produces an equal depth of abrasion with the same force, its hardness is said to be 4; if with more facility than 4 but less than 5, the hardness may be 4∣ or 4⅜, written in decimals 4 ’ 25, 4 ’ 5. Several successive trials should be made to obtain certain results.

The use of the file is acquired with very little experience; usually a single trial is sufficient. Care must be taken to apply the file to edges of equal obtuseness. That part also of the specimen should be selected which has not been altered by exposure, and has the highest degree of transparency and compactness of structure. The pressure for determination should be rather heavy, and the file should be passed three or four times over the specimen.

Where the scale of hardness is wanting, or a first rough determination is sought, the following experiments may serve :—

Every mineral that is scratched by the finger-nail has H. = 2 , 5 or less. Minerals that scratch copper have H. = 3 or more. Polished white iron has H. = 4 5. Window-glass has H. =5toδ - 5. Steel point or file has H. = 6 to 7; hence every mineral that will cut or scratch with a good penknife has H. less than 6. Flint has H. =7, and only about a dozen minerals, including the precious stones or gems, are harder.

Many specimens present different degrees of hardness on dissimilar faces; as an example of which we mention cyanite and mica. This is confined to the inequilateral primary forms, and like the similar difference of colour, lustre, &c., finds a ready explanation in the theory of their formation; unlike faces are the result of the action of a polar force acting along unlike axes.

This difference in faces parallel to unlike axes may be perceived in nearly all cases, when the methods of trial are sufficiently delicate. Huygens observed long ago that the cleavage face of a crystal of calc-spar differed in hardness from the other faces; and even in a mononιetric crystal it has been found that the faces of the cube and octahedron are not exactly alike in this respect.

2. Tenacity.— Solid minerals are said to be brittle, sectile, malleable, flexible, or elastic :—

1. Brittle, when parts of a mineral separate in powder or grains on attempting to cut it; as baryte, calc-spar.

2. Sectile, when pieces may be cut off with a knife without falling to powder, but still the mineral pulverizes under a hammer; as brucite, gypsum.

3. Malleable, when slices may be cut off, and these slices flatten out under a hammer; as native gold, native copper.

4. Flexible, when the mineral will bend and remain bent after the bending force is removed; as gypsum, graphite, talc.

5. Elastic, when after being bent it will spring back to its original position; as mica,

A liquid is said to be viscous when, on pouring it, the drops lengthen and appear ropy; as petroleum.

3. Elasticity.— Investigations on this property have not to any extent been entered upon. The unequal elasticity of unlike faces of crystals has been shown by Savart in his acoustic investigations, and he was able to distinguish the rhombohedral from the other faces in the pyramid of quartz crystals; he also showed that the figures formed upon vibrating plates of crystals were directly connected with their optic axes. Milne, by measuring the amount of recoil of a sphere of calcite when struck at different points by another of rock-crystal, found that the elasticity, as thus measured, was greatest along the line of the optic axis, and least in directions at right angles to it. He also found that points which lay intermediate between the main and the transverse axes were most indented by the blows. This goes to show that, although there may be fewest molecules arranged along the lines of the transverse axes, yet cohesion operates with greater intensity along these than in intermediate directions.

When the tenacity of a mineral is overcome by an overwhelming amount of traction, or its elasticity by a sudden shock, its parts are separated, either in flat and continuous surfaces, or in surfaces which are irregular in the extreme. The first of these modes is termed cleavage, the second fracture. In those substances in which cleavage exists it is found that the planes or directions along which it takes place lie in certain strictly definite positions to one another and to the axes of the crystal. They show not the smallest tendency to a transition or gradual passage into the other directions of greater coherence.

4. Cleavage.— The number of these parallel cleavageplanes is altogether indefinite, so that the only limit that can be assigned to the divisibility of some minerals, as gypsum and mica, arises from the coarseness of our instruments. These minima of coherence, or cleavage-planes, are always parallel to some face of the crystal; and similar equal minima occur parallel to every other face of the same form. Hence they are always equal in number to the faces of the form, and the figures produced by cleavage agree in every point with true crystals, except that they are artificial. They are thus most simply and conveniently described by the same terms and signs as the faces of crystals.

Some minerals cleave in several directions parallel to the faces of different forms, but the cleavage is generally more easily obtained and more perfect in one direction than in the others. This complex cleavage is well seen in calc-spar and fluor-spar, and very remarkably in zinc blende, where it takes place in no less than six directions. As in each of these the division may be indefinitely continued, it is clear that no lamellar structure in any proper sense can be assigned to the mineral. All that can be affirmed is that contiguous atoms have less coherence along a direction normal to these planes than in other directions. When cleavage takes place in three directions, it of course produces a perfect crystal form, from which the system of crystallization and angular dimensions of the species may be determined; it is thus often of very great importance.

The common cleavage in the different systems is as follows, those of most frequent occurrence being in italics :—(1) In the cubic system, Octahedral, 0, along the faces of the octahedron; Hexahedral, ooOoo, along those of the cube; and Dodecahedral, ∞O. (2) In the tetragonal system, Pyramidal, P, or 2Pα>; Prismatic, ∞P, or ∞P∞; or Basal, OP. (3) In the hexagonal system with holohedral forms, Pyramidal, P, or P2; Prismatic, ∞P, or ooP∞; or Basal,QP∙, with rhombohedral forms, Rhombohedral, R; Prismatic, α>R; or Basal, OR. (4) In the right prismatic system, Pyramidal, P; Prismatic, ooP; Macrodomatic or Brachydomatic, f 5 ∞ or P∞; Basal, OP; Macrodiagonal, ∞P∞; or Brachydiagonal, α>P∞. (5) In the oblique prismatic system, Hemipyramidal, P, or - P; Prismatic, ooP; Clinodomatic, P c ∞; Hemidomatic, Γ 0 α> or - P 0 oo; Basal, OP; Orthodiagonal, o°P o α>; or Clinodiagonal, α>P e oo. (6) In the anorthic system, Hemiprismatic, α>P , , or α>P; Hemidomatic either along the macrodome or the brachydome; Basal, OP; Macrodiagonal, oo Poo; or Brachydiagonal, oopoo.

In some minerals, as mica and gypsum, the cleavage is readily procured; these may be held in the hand and divided by a knife. Others only cleave with more or less difficulty; these must be placed on a firm support resting on lead, folded paper, or cloth, and a sharp blow struck on a chisel applied in a proper direction. This may often be ascertained by examining the specimen in a strong light. Sometimes it is necessary to subject them to extreme compression in a vice. Some of the hardest substances have not only a perfect but a facile cleavage,—as euclase, topaz, and diamond; many of the softest species have none. The planes produced also vary much in their degree of perfection, being highly perfect in some, as mica and calc-spar, and imperfect in others, as garnet and quartz. In a very few crystalline minerals cleavage-planes can hardly be said to exist. Cleavage must be carefully distinguished from the planes of union in twin crystals, and the division-planes of laminar minerals.

5. Fracture.— This is the irregular manner in which substances may be broken. Even minerals possessed of cleavage may be fractured in other directions; but in amorphous bodies fracture alone occurs. The following varieties of fracture occur, and are highly characteristic:—

1. Conchoidal, almost typical of amorphous bodies, but occas-sionally seen in crystals,—rounded cavities, more or less deep. The name is taken from the resemblance to the successive lines of interrupted growth in a bivalve shell. Seen in flint, obsidian, asphalt. In calcite the direction of this fracture is intermediate to the planes of the mineral’s cleavage.

2. Even, when the surface of fracture is smooth and free from inequalities.

3. Rough, when the surface of fracture is rugged, with numerous small elevations and depressions.

4. Splintery, when covered with small wedge-shaped splinters.

5. Hackly, when the elevations are sharp, slightly bent, or jagged, as broken iron.

6. Earthy, when it shows only fine dust.

Taste, Odour, Touch. Taste belongs only to soluble minerals. The different kinds adopted for reference are as follows :— [table]

Odour.— Excepting a few gaseous and soluble species, minerals in the dry unchanged state do not give off odour. By friction, moistening with the breath, and the elimination of some volatile ingredient by heat or acids, odours are sometimes obtained which are thus designated :—

1. Alliaceous, the odour of garlic. Friction of arsenical iron elicits this odour; it may also be obtained from any of the arsenical ores or salts by means of heat.

2. Horse-radish odour, the odour of decaying horse-radish. This odour is strongly perceived when the ores of selenium are heated.

3. Sulphurous. Friction will elicit this odour from pyrites, and heat from many sulphurets.

4. Bituminous, the odour of bitumen.

5. Fetid, the odour of sulphuretted hydrogen or rotten eggs. It is elicited by friction from some varieties of quartz and limestone.

6. Argillaceous, the odour of moistened clay. It is obtained from serpentine and some allied minerals after moistening them with the breath; others, as pyrargillite, afford it when heated.

7. Empyreumatic or ozonic. Quartz, when two portions strike one another.

Touch.— Some minerals are distinguished by a greasy feeling, as talc; others feel smooth, as celedonite; others meagre, like clay; others cold. This last character distinguishes true gems from their imitations in glass. Some, in virtue of their hygroscopic nature, adhere to the tongue.

Chemical Properties of Minerals. Influence of Chemical Composition on the External Characters of Minerals.— That the characters of a compound must to a certain extent depend on those of its component elements seems, as a general proposition, to admit of no doubt. Hence it might be supposed possible from a knowledge of the composition of a mineral to draw conclusions in reference to its form and its other properties; but practically this has not yet been effected.

The distinction between the mineralizing and mineralizable or the forming and formed elements lies at the foundation of all such inquiries. Certain elements in a compound apparently exert more than an equal share of influence in determining its physical properties. Thus the more important non-metallic elements, as oxygen, sulphur, chlorine, fluorine, are remarkable for the influence they exert on the character of the compound. The sulphurets, for example, have more similarity among themselves than the various compounds of one and the same metal with the non-metallic bodies. Still more generally it would appear that the electro-negative element in the compound is the most influential, or exerts the greatest degree of active forming power. After the non-metallic elements the brittle, easily fusible metals rank next in power; then the ductile ignoble metals; then the noble metals; then the brittle, difficultly fusible; and, last of all, the metals of the earths and alkalies.

Generally each chemical substance crystallizes only in one form or series of forms. Some substances, however, show dimorphism, or crystallize in two forms, and thus may compose two or more minerals. Thus sulphur, which in nature usually crystallizes in the right prismatic system, when melted forms oblique prismatic crystals. Carbon in one form is the diamond, in another graphite; carbonate of lime appears as calc-spar and as aragonite; the bisulphuret of iron as pyrite and as marcasite. An example of trimorphism occurs in titanic acid, forming the three distinct species anatase, rutile, and brookite. It is remarkable that of dimorphic minerals one form is almost always right prismatic; thus:— [table]

Even the temperature at which a substance crystallizes influences its forms, and so far its composition, as seen in aragonite, Glauber salt, natron, and borax.

Isomorphism.— Still more important is the doctrine of isomorphism, designating the fact that two or more simple or compound substances crystallize in one and the same form, or often in forms which, though not identical, yet approximate very closely. This similarity of form is generally combined with a similarity in other physical and in chemical properties. Among minerals that crystallize in the tesseral system, isomorphism is of course common and perfect, there being no diversity in the dimensions of the primary form; but for this very reason it is generally of less interest. It is of more importance among crystals of the other systems, the various series of which are separated from each other by differences in the proportions of the primary form. In these perfect identity is seldom observed, but only very great similarity.

The more important isomorphic substances are either simple substances, as (1) fluorine and chlorine; (2) sulphur and selenium; (3) arsenic, antimony; (4) cobalt, iron, nickel; (5) copper, silver, mercury, gold (?); or combinations with oxygen, as (6) lime, magnesia, and the protoxides of iron, manganese, zinc; (7) sesquioxides, as of iron, manganese, chromium, and alumina; (8) phosphoric acid, vanadic acid, arsenic acid; (9) sulphuric, selenic, chromic acids; or combinations with sulphur, as (10) sulphuret of iron and of zinc; (11) sulphuret of antimony and of arsenic; (12) sulphuret of lead, of copper, and of silver. These substances are named vicarious from the singular property that in chemical compounds they can mutually replace each other in definite proportions, and very often without producing any important change in the form or other physical properties. But there are numerous instances among the silicates where the mutual replacement of thβ>isomorphic bodies, especially when the oxides of the heavy metals come in the room of the earths and alkalies, exerts a most essential influence on the external aspect of the species, particularly in regard to colour, specific gravity, and transparency. The varieties of hornblende, augite, garnet, epidote, and many other minerals are remarkable proofs of this influence. This intermixture of isomorphic elements confers many valuable properties on minerals, and to it this department of nature owes much of its variety and beauty. Without the occasional presence of the colouring substances, especially the oxides of iron and manganese, the non-metallic combinations would have exhibited a very monotonous aspect. It is also remarkable that in some silicates the substitution of a certain portion of the metallic oxides for the earthy bases seems to be almost a regular occurrence; whilst in others, as the felspars and zeolites, this rarely happens. This fact is also of great economic interest, as drawing attention to important elements often combined with others of less value. Thus iron oxide and chrome oxide, sulphuret of copper and sulphuret of silver, nickel and cobalt, may be looked for in connexion. The general chemical formulae for such compounds is formed by writing R ( = radical or basis) for the whole isomorphic elements; and in special instances their signs are placed one below the other, connected by a bracket, or, as is more convenient, are enclosed in brackets one after the other separated by a comma. Thus the general sign for the garnet is R 3 Si 2 + R Si, which, when fully expressed, becomes (Ca 3 , Fe 3 , Mg 3 , Mn 3 ) Si 2 + (⅛1, ⅛⅛, θr)Sij and this mineral forms many varieties as the one or other element preponderates.

Of the forms special to similar groups of atoms the more notable are—the cubic system, special to metals proper, and binary compounds as protoxides and haloid salts; the tetragonal to binoxides; the rhombohedral to carbonates; the hexagonal to sesquioxides and phosphates and their isomorphs; the prismatic to sulphates and their isomorphs.

The isomorphism of minerals goes as a whole to show that form depends on the number of molecules present, and is comparatively little influenced by the nature of the molecules themselves.

DESCRIPTION OF MINERAL SPECIES.

The arrangement adopted in the following description of mineral species is chemical. Simple substances are considered first, in the order of their quantivalence, then binary compounds, and lastly those of more complex structure. Our limits permit of the briefest notice of the less important, in order that more space may be available for the delineation of the characteristic and transition forms of such as go to constitute the more important rock masses.

The following abbreviations are used:—H., hardness; G., specific gravity (distilled water at 60° Fahr, and barometer 30 inches =1); cl., cleavage; sol., soluble; s. [h. or n.] acid, sulphuric [hydrochloric or nitric] acid; B.B., before blowpipe; ox., oxidizing; red., reducing; c.c., chemical composition; com., combination.

In the chemical formulae, barred letters express two equivalents, and the dots over the symbols indicate the combination with them of as many equivalents of oxygen as there are dots.

In the symbolic notation the several faces of crystals are separated by semicolons, and the constituent members of combinations by commas. The lettering on the faces of the figures is for the most part that adopted by Miller. In the enumeration of crystal forms, that which is typical of the mineral is placed first.

SIMPLE SUBSTANCES.

1. Sulphur, S.

(a) Right prismatic. P (p) polar edges 106° 38', 84° 58', middle edge 143° 17'; «P 101° 58'; OP (c); iP(s); Poo (n ). Crystals pyramidal, single or in druses; also stalactitic, disseminated, and pulverulent. Cl. basal and α>P. H. = 1 , 5 to 2 5; G. =19 to 2 ’ 1. Fracture conchoidal or splintery; brittle, sectile. Lustre resinous, streak and colour sulphur-yellow, passing into red, brown, or green. Sublimes in the closed tube. Fuses a little above the temperature of boiling water. Takes fire at 518° F., and burns with a pale blue flame with odour of sulphurous acid. C.c.: pure sulphur, occasionally mixed with traces of selenium, and when amorphous with clay or bitumen. Found chiefly in Tertiary strata. Localities: Girgenti in Sicily, with celestine; Conil in Spain; Bex in Switzerland; Cracow in Poland; deposited from hot springs in Solfatara near Naples; from hot springs in Iceland; from sulphur springs in New York; and in cavities of decomposing galena, cinnabar, and pyrites at several localities.

(5) Oblique prismatic. The crystals of volcanic sulphur are of this form; they occur in the neighbourhood both of extinct and of recent volcanoes. They are slender, needle-shaped, and interlacing, and have generally more or less of a red-brown tinge. Oxhaveer and Cape Reykjanes in Iceland, Sicily, and the volcanoes of the Pacific, the Chilian Andes, and California yield this variety.

2. Selensulphur, S.Se.

Like sulphur, but reddish brown to orange-yellow. B. B. burns with fumes of selenious acid mixed with the sulphurous. Found in the crater of Volcano in the Lipari Islands, and Kilauea in Hawaii.

3. Selenium, Se.

H. = 2; G. =4 ’ 3. Brownish black to lead-grey; thin splinters translucent and red. From Culebras in Mexico.

4. Tellurium, Te.

Rhombohedral; R 86° 50'. In minute hexagonal prisms, with basal edges replaced; usually massive and granular. Cl. lateral perfect, basal imperfect. H. = 2 to 2‘5; G. = 6 ’ 1 to 6 ’ 3. Tin-white; sectile. C.c.: tellurium with a little gold and iron. Occurs at Facsebaya near Zalathna (Transylvania), and in several mines in Boulder county, Colorado; masses 25 lb in weight have been obtained there.

5. Arsenic, As .

Rhombohedral; R 85° 36' (fig. 258). Usually in botryoidal investing masses composed of numberless layers. The structure is fine granular, rarely columnar. H. = 3 ‘5; G. = 5 ’ 7 to 5 - 93. Cl. basal. Colour black and dull, but when fresh broken very splendent and silver-white; fracture uneven. When rubbed or heated gives out a garlic-like odour. B. B. volatile, with formation of white fumes. C.c.: arsenic, with some antimony, and traces of iron, silver, and gold. Andreasberg in the Harz, Annaberg, Schneeberg, Freiberg, Joachimsthal, Allemont (Dauphine), Kongsberg (Norway), the Altai, Chili, Pebble mine (Dumfriesshire), Tyndrum (Perthshire).

6. Antimony, Sb.

Rhombohedral; R 87° 35'; but rarely crystallized, generally in foliated or granular masses. Cl. basal. H. = 3; G. = 6 6 to 6 ‘8. Tin-white, with slight yellow tarnish. Brittle and sectile. B. B. easily fusible; volatilizes, and on charcoal leaves a white deposit, burning with a pale flame. Found at Andreasberg, Przibram (Bohemia), Sala (Sweden), Allemont, Southham in East Canada, and Borneo.

7. Allemontite, SbAs 3 .

Hexagonal, spherical, reniform, and investing. H. = 3 - 5; G. = 6 1 to 6 ’ 2. Lustre, when fresh, metallic. Tin-white to lead-grey, but with ablue or brown tarnish. B.B. strong odour of garlic, with residuum of oxide of antimony. C.c.: antimony 37‘85, arsenic 62 ’ 15. Almost always in curved foliated laminae. Occurs at Allemont, Przibram, Schladming in Styria, Andreasberg.

8. Bismuth, Bi.

Rhombohedral; R 87° 40'. Crystals, R,0R, generally distorted; also reticulated, spear-head twins, or arborescent; also disseminated and granular. Cl. basal, perfect. H. =25; G. = 96 to 9 ’8. Brittle and sectile. Reddish white, often tarnished grey, brown, or blue. B.B. easily fusible, even in candle flame. Volatilizes on charcoal, leaving a citron-yellow crust. Sol. in n. acid; solution precipitated when thrown into water. Occurs in gneiss and clay slate in veins and disseminated, along with ores of cobalt, silver, lead, and zinc. Alva in Stirlingshire, Cumberland, Devonshire and Cornwall, Schneeberg, Marienberg, Joachimsthal, Bieber, Modum (Norway), Falun (Sweden), Bolivia.

9. Telluric Bismuth, Bi 2 Te 3 .

Bismuth 52, tellurium 48. Virginia, Dahlonega in Georgia, Montana. A variety with 7 per cent, of selenium and H. = 2 also occurs.

10. Tetradymite, Bi 2 Te 2 S.

Rhombohedral; 3R 68° 10'. Almost always twins of 3R and OR, with the faces of OR at 93°. Cl. basal, perfect. Sectile, and thin laminae flexible. H. = 1 to 2; G. =7 ’ 2 to 7'5. Steel-grey. B.B. fuses, yielding a grain of metal which ultimately volatilizes. Sol. in n. acid. C.c.: 59’6 bismuth, 35'9 tellurium, and4 ’ 5 sulphur. Schemnitz.

11. Wehrlite, Bi(Te 8 S).

Hexagonal. Cl. basal. H. = 1 to 2; G. = 8'44. High lustre. Steelgrey. C.C.: bismuth 6115, tellurium 29'74, sulphur 2'33, silver 2Ό7. Deutsch-Pilsen in Hungary.

12. Joseite, Bi s Te 2 (SSe) 2 .

Hexagonal. Cl. basal. G. — 7'93. Colour grey-black to steelgrey. Brittle. C.c.: tellurium 15'93, sulphur 315, selenium 1∙48, bismuth 79'15. San José (Brazil). A Cumberland variety yielded tellurium 6'73, sulphur 6'43, bismuth 84'33, corresponding to Bi 4 (TeS 4 ).

13. Diamond, C.

Var. 1. Crystallized. — Cubic; very frequently hemihedral. Crystals most generally with curved faces. Twins common on the octahedral face; hemitropes also common (see tigs. 170, 204, 205, 207). Crystals vary remarkably in appearance (see figs. 259 to 262). Cl. octahedral. H. = 10; G. — 3 '5 to 3 '6. Transparent, or translucent when of dark colour. Refracts light strongly. The back planes of diamonds reflect all the light which strikes them at an angle exceeding 24° 13', and thence comes their peculiar brilliancy. High adamantine lustre. Colourless, but often tinged white, grey, and brown,—more rarely yellow, pink, blue, green, and black, those last named being the rarest. Disperses light highly, and hence emits brilliant flashes of all the colours of the spectrum. Becomes positively electric by friction. B.B. infusible, but burns into carbonic acid in oxygen gas. When air is excluded is unchanged at the temperature of melting cast iron, but at that of melting malleable iron is changed into a black coke, or, it is said, into graphite. Insoluble in all acids and alkalies. C.C.: carbon, with traces of silica and earths. Geologic formation apparently a laminated flexible quartz rock called itacolumite, which occurs in Brazil, the Urals, Georgia, and North Carolina, in the vicinity of places where diamonds have been found. Minute crystals have been found in xanthophyllite, and in talc slate and serpentine, in the Schischim-skian hills, near Zlatoust (Russia). They have also been obtained in Brazil imbedded in a conglomerate composed of much-worn pebbles of quartz, chalcedony, and gold, cemented by limonite or ferruginous clay. In South Africa they are imbedded in a steatitic clay. Diamonds were formerly obtained in India, at Panna, Raol-conda, and Golconda. So few are now obtained here that the mines are let for £1 a year. From these mines were obtained not only the Kohinoor, which was possibly the same as the great diamond mentioned by Tavernier as having been seen by him in the possession of the Great Mogul, which weighed 280 carats, but the Regent, of 136 carats (which, not only from its size, but from the perfection of its form, is very much the finest diamond known), the Nizam, an uncut diamond of 340 carats, and the Carlow, rosecut, 193 carats. More lately diamonds were found in great quantity in the neighbourhood of Rio Janeiro in Brazil; they occur in two different deposits: the one called “gurgulho” consists of broken quartz covered by a bed of sand; the other, “cascalho,” consists of rolled quartz pebbles united by ferruginous clay; both rest on talcose clays, which are the debris from talcose rocks. The first deposit affords the finest diamonds, and both contain gold, platinum, magnetite, and rutile. A dodecahedral diamond of 257 carats was lately found at Bogagem in this district; this was reduced by cutting to an oblong brilliant of 125 carats, and is the second most valuable diamond,—the Kohinoor, now reduced to an imperfectly circular brilliant of 102 carats, occupying the third place. The two coloured diamonds most worthy of note are a green diamond in the Dresden collection weighing 31 carats, which is a little deeper in tint than a beryl, and a blue diamond in the Hope collection, of 44 carats, as highly coloured as a sapphire, which it is by some considered to be. Diamonds have lately been found in very large quantities, and some of great size, north of the Cape of Good Hope; these for the most part are of yellow colour and of very inferior value. While a Brazilian cut brilliant of one carat is worth from £20 to £25, the value of the finest brilliants from the Cape is only from £3 to £4, and that of the yellow diamonds is from £2 to £2, 10s. Apart from its employment as an ornamental stone, the diamond has an intrinsic value from its being utilized for cutting glass and for grinding and polishing other gems. Of late years its usefulness has had a new application, it being employed for the drilling of rocks in tunnelling operations and in the boring of artesian wells. A singular observation has resulted from these last methods of utilizing it, namely, that the hardness of the African diamonds, as tested by the amount of their endurance, is markedly inferior to that of the Brazilian and Indian. So much is this recognized that, while the bort, or minute crystals, of the latter command aprice of 15s. per carat, the African can be got for about 5s. The cleavage of certain of the African diamonds is so eminent that even the heat of the hand causes some of them to fall in pieces. Such diamonds, generally octahedra, may be recognized by a peculiar watery lustre; they are called plate diamonds. The above facts give some ground for the supposition that there may be a slight difference in their composition, possibly that both may contain small, but different, quantities of hydrogen. The circumstances under which diamonds have been formed are altogether unknown. The fact of their being changed into a kind of coke at a very high temperature is an argument against their having been produced through the operation of heat, and it has long been known that an excess of carbon dissolved by molten cast iron crystallizes on cooling in the form of graphite; yet the only attempts to form diamonds deserving of being mentioned as having been attended with any measure of success are those in which sugar charcoal was dissolved in molten silver at the temperature only or melting steel. There were thus obtained a few minute black and also colourless octahedral and cubo-octahedral crystals with curved faces, mingled with a much larger amount of graphitoidal carbon.

Var. 2. Massive.— In black pebbles or masses called carbonado, sometimes 1000 carats in weight. H. = 10; G. =3'012 to 3'42. C.c.: carbon except '27 to 2 07 per cent, of ash. Found in the mines of Baranco, &c., in Bahia.

Var. 3. Anthracitic.— Like anthracite, but scratches the diamond. In mammillar masses, partly in concentric layers, and globular. Brittle. G. = 1 '66. C.c.: carbon 97, hydrogen '5, oxygen 1 5. When cut and polished, refracts and disperses light, like the diamond. Supposed from Brazil.

14. Graphite, C.

Hexagonal in flat crystals; p:p 85° 29'. Usually foliated, scaly, or compact. Cl. basal. H. = 0 '5 to 1; G. = 1 '9 to 2 '2. Lustre metallic. Colour and streak black to dark steel-grey; flexible in thin laminae; very sectile; feels greasy; leaves a mark on paper of its own colour; conducts electricity. B.B. burns with difficulty; heated with nitre, deflagrates. C.c.: carbon, with small quantities of volatile matter, and ash from 5 to 40 per cent. Strathfarrer (Inverness-shire), Mull, Craigman (Ayrshire), Borrowdale in Cumberland, Ural Mountains, Ceylon, Greenland. Used for making pencils.

15. Tin, Sn.

Tetragonal in greyish white metallic grains. Reported as occurring with Siberian gold; with bismuthite from Guanajuato in Mexico.

16. Iron, Fe.

Cubic; in grains and plates or disseminated. H. = 4 '5; G. = 1 to 7'8. Steel-grey or iron-black. Fracture hackly, very magnetic. B.B. infusible. Sol. in h. acid. Two varieties are to be distinguished, (a) Telluric Iron, in grains and plates. Almost pure iron, or contains graphite, carbon, lead, or copper, but no nickel. At Chotzen in Bohemia in limestone; in an argillaceous sandstone in the keuper at Mühlhausen; in Thuringia along with fossils; in an ironstone conglomerate in Brazil, and in lava in Auvergne; in the mine of Hackenburg; at Bexley, in Liberia, Africa, along with quartz, a zeolite, and magnetite; enclosed in magnetite in Unst (Shetland) and in Sutherlandshire; in basalt in Antrim, Ireland; in the gold sands of Brazil, the Urals, and Olahpian (Transylvania). (&) Meteoric iron, steel-grey tqøilver-white.

Almost always contains nickel, with cobalt, copper, and several minerals which are non-terrestrial. When polished and etched with nitric acid the surface is marked by lines of unaffected interlacing crystals called Widmannstatten’s figures; most of the nickel is contained in these. Occurs in masses which vary in size from the smallest microscopic dust as dredged from the depths of the ocean to upwards of 32,000 lb. Many of these masses have been seen to fall. Several (suspected, however, to be terrestrial) have been found imbedded in a basaltic rock near Disco Bay in Greenland, one of which is 44,000 lb in weight. Several contain hydrogen in their pores, condensed to the extent of eight times the volume of the mass; and the pitted depressions frequently observable upon their surface give countenance to the view that, if not discharged from a volcanic throat, they were set at liberty by some sudden disrupting gaseous explosion.

17. Zinc, Zn .

Rhombohedral. Said to be found in large hexagonal pyramids. Cl. basal, perfect. H. = 2; G. = 7. Lustre metallic. Colour and streak bluish white. Found in a geode in basalt near Melbourne, Australia, coated with smithsonite, erythrine, and aragonite. Also in the gold sands of the Mittamitta river.

18. Copper, Cu.

Cubic (figs. 28, 30, 26, 33, 37, 264). Twins, on an octahedral face. Crystals generally distorted. Often filiform and arborescent, or in platesand laminae. H. =2’5 to 3; G. =8’5 to 8’9. Lustre dull metallic. Colour and streak copper-red, with yellow or brown tarnish. B. B. easily fusible, colouring the outer flame green.

Sol. in n. acid. Occurs in many rocks (generally igneous), and frequently associated with zeolites. In the Faroes, Unst (Shetland), Cornwall, Chessy near Lyons, the Banat (Hungary), Siberia, China, Mexico, Brazil, Chili, and Australia. Masses of great size are found, much the largest being from the Ontanagon river, on the south of Lake Superior. One mass found in February 1857 was 45 feet in length, 22 feet in width, and 8 feet in thickness; its weight was 420 tons. Another was found in 1869, 65 feet in length, 32 in width, and from 4 to 7 feet in thickness; this weighed upwards of 1000 tons, and had a value of 400,000 dollars.

19. Lead, Pb.

Cubic, but only in thin plates, capillary or filiform. Cl. none. H. =1*5; G. =ll - 36 to 11’4. Ductile, malleaole, and sectile. Bluish grey, but with a blackish tarnish. Found in lava in Madeira, and at the mines near Cartagena in Spain; in amygdaloid near Weissig; in basaltic tufa at Rautenberg in Moravia; with gold near Mount Alatau in the Altai, at Velika in Slavonia, and at Olahpian in Transylvania; near Ekaterinburg in the Urals; in the district of Zomelahuacan in Vera Cruz, in foliated galena, in granular limestone'; in the iron and manganese bed of Paisberg in Wermland (Sweden), with haematite, magnetite, and hausmannite; in white quartz, north-west, near the Dog Lake of the Kaministiquia, an affluent of Lake Superior; imbedded in hornstone in plates and grains, in the mine of Bogoslovskoi in the Kirghiz steppes; in greenstoneporphyry at Stützerbach in Thuringia; with haematite in the islands of Nias on the west coast of Sumatra.

20. Mercury, Hg.

Cubic. Occurs in small liquid globules in its gangue, but may be solidified at - 39°, when it forms octahedral crystals. G. = 13’596 when liquid, 15’612 when solid. Lustre brilliant metallic; tin-white. B. B. volatile, sometimes leaving a little silver. Readily sol. in n. acid. Occurs generally in clay shales or schists of different ages. The globules of mercury are usually found in rents in cinnabar, or accompanying calomel, at most of the localities for these minerals. Found at Idria in Carniolaand Almaden in Spain. At Idria it is obtained by washing a soft clay slate. In Transylvania and Galicia springs issuing from the Carpathian sandstone bear along globules of mercury. At the Pioneer mine in California some of the quartz geodes contain several pounds of mercury. At Cividale in Lombardy it is found in an Eocene marl. ,. It has also been observed occasionally in drift, and has even been stated to have been found in a peat bog.

21. Silver, Ag.

Cubic (figs. 26, 30, 33, 40, 37). Crystals generally small, also and most frequently filiform, arborescent, and in plates or crusts. These either project into cavities, coat their surfaces, or ramify in a reticulated manner throughout the mass of the rock. Twins of octahedral and trapezohedral composition. Noel. H. =2’5 to 3; G. =10’1 to 11Ί. Lustre metallic. Colour and streak silver-white, but generally tarnished yellow, brown, or black. Malleable, ductile, and sectile, but less so than gold. B. B. easily fusible. Sol. in n. acid; the solution colours the skin black. C.c: silver, with varying proportions of gold, platinum, mercury, copper, antimony, and bismuth. The auriferous from Norway contains silver 72, gold 28; from quartz reefs in Sutherland, silver 7Γ4, gold 28’6. The cupriferous from Courcy near Caen contains 10 per cent, of copper. The antimonial from Bohemia contains 1 per cent, of antimony. The mercurial from Kongsberg in Norway has ’ 4 of mercury, found chiefly in veins in gneiss, clay slate, and limestone. Localities: Alva and elsewhere in Scotland, Ballycorus in Ireland, and Cornwall in England; at Freiberg, Andreasberg, and Kongsberg; along with native copper at Lake Superior; in Mexico, in Peru, and in the United States. The finest crystallized silver occurs at Lake Superior, and at Kongsberg. At the last locality the crystals are an inch in diameter, and are disposed on large filiform brushes. Silver occurs in large masses; three of 436, 560, 812 lb have been recorded from Kongsberg. A block which smelted 44,000 lb was for some years used as a table by Duke Albert on his annual visits of inspection to the Schneeberg mine in Saxony. A Mexican specimen was found of 400 lb; the mines of Huantaya in Peru have yielded masses of 444 and 960 lb. Britain produces annually about 760,000 oz. of silver, chiefly, however, from lead ores. The value of annual produce for the whole world from all sources is from 8 to 10 millions of pounds sterling.

22. Schneiderite (Gold Amalgam), Au 2 Hg 3 .

Tetragonal four-sided prisms, easily crumbling, yellowish white to white; sometimes in grains the size of a pea. C.c.: gold 41’63, mercury 58’37. Found at Mariposa in California. A variety (Au, Ag) 2 Hg 5 is found along with platinum in Columbia; this contains gold 38’39, silver 5, mercury 57’40.

23. Arquerite, Ag 6 Hg.

Cubic. In octahedra, also in grains and dendrites. G. = 10’8. Like native silver, but softer. C.c.: silver 86’5, mercury 13’5. From Arqueros in Coquimbo, Chili. Kongsbergite, Ag 18 Hg, occurs at Kongsberg, with 95 Ί of silver and 4 - 9 of mercury.

24. Amalgam, Ag.Hg 2 , andAgHg 3 .

Cubic (fig. 33, in combination with 40, 30, 41, 38). Cl. dodecahedral. H. =3 to 3’5; G. =10’5 to 14. Colour and streak silver-white. Fracture conchoidal, brittle, grates when cut. In closed tube yields mercury and leaves silver. Sol. in n. acid. The first variety (silver 34’8, mercury 65’2) occurs at Moschellandsberg in the Palatinate, where the veins of mercury and silver intersect one another; the second (silver 26’25, mercury 73’75) there, and also at Allemont in Dauphiné, Almaden in Spain, in Hungary, and in Sweden. From Rosilla in Atacama (Chili) Domeyko reports the following other compounds: Ag 3 Hg 4 , silver 46’8, mercury 53’2, white and silvery; AgHg, silver 55’1, mercury 44’9, granular and dull; Ag 5 Hg 3 , silver 64’2, mercury 35’8; of the last there is a mass weighing 22 lb in the museum of Santiago.

25. Gold, Au.

Cubic (figs. 30, 26, 33, 40, 36) and more complex forms. Crystals generally small and indistinct through elongation, assuming capillary and arborescent shapes. Also in thin plates. Twins rare; twin face octahedral. Frequently in rounded and apparently colloidal masses impacted in clay, or loose in small grains (pipettes) rolling in the bed of streams. Fig. 265 is of such a mass found in Sutherland. No cl. H. =2’5 to 3; G. = 17 to 19’4. Lustre metallic, but frequently dull and partly coated with a brown crust.

Colour and streak yellowish white to bright gold-yellow. Malleable, ductile, and sectile; the purer varieties the more so and the softer. B.B. easily fusible. Sol. in aqua regia, generally with precipitation of chloride of silver. Solution yellow, stains skin purple-red, with corrosion.

C.c.: gold, with silver from ’ 72 to 26 per cent.; sometimes iron and copper under 1 per cent. Found in beds and veins generally of quartz in metamorphic rocks of a schistose nature, rarely in diorite and porphyry, and very rarely in granite. Its general associate is limonite, formed from decomposition of pyrite; sometimes also haematite and magnetite. Occurs also in microscopic grains in quartz, from which it is extracted by crushing and amalgamation. The geologic range is from the Azoic to the Tertiary and Cretaceous, as in California; but even in these more recent rocks the original source must have been at least Palaeozoic. Of localities which yield gold the following may be noticed :—the Leadhills in Scotland, Wicklow in Ireland, Dolgelly in North Wales, Cornwall in England; Transylvania, Hungary, and Piedmont; the Urals, Ekaterinburg, and India; Kordofan, the coast opposite Madagascar, and the Gold Coast (the fame of which has been recently revived); Minas Geraes in Brazil, Bolivia, North Carolina, and California; and more recently New South Wales and Queensland in Australia, Tasmania, and New Zealand.

Some of the largest single masses of gold found in recent times are the following:—one of 22 oz. in Transylvania, of 28 lb in North Carolina, of 20 lb in California, one of 96 lb troy near Miask in the Urals, and one of 184 lb 8 oz., which yielded £8376, 10s. 6d., at Ballarat, Australia.

The annual produce of gold from Australia is about 5 millions of pounds sterling, of the United States about 15 millions, and the whole earth about 23 millions.

The following sub-species may be noticed :—

1. Electrum. This name for the alloys of gold and silver was applied by Pliny, whenever the proportion of the latter metal was one-fifth. An alloy of 2 gold and 1 silver contains 21 per cent, of silver; this is found in Sutherland. One of 1 to 1 contains 86 per cent, of silver, this last being the most usual proportion. It occurs in Transylvania, in the Altai, and in Colombia. Its colour is brass-yellow to yellowish white. G. = 12'5 to 15'5.

2. Porpezite, or Palladium Gold (ouro-poudré), from Porpez in Brazil, contains 9'85 per cent, of palladium and 4'17 of silver.

3. Rhodium Gold, from Mexico (G. =15'5 to 16'8), contains from 34 to 43 per cent, of rhodium.

26. Platinum, Pt.

Cubic; rarely in small cubes or octahedrons, usually in minute scaly grains, sometimes cohering, and also in rounded lumps. No cl. H. = 4 to 4 '5; G. = 17 to 19. Lustre metallic. Colour and streak pale steel-grey. Malleable and ductile with difficulty, having a hackly fracture. When containing much iron, magnetipolar. B. B. infusible. Sol. iu aqua regia, but only when heated; solution red; corrodes the skin. C.c.: platinum, but never to a greater extent than 86 '5 per cent. The remainder consists of iron, iridium, rhodium, palladium, osmium, gold, copper, and a mechanical mixture of iridosmine. The iron exists in quantities varying from 4 '3 per cent, to double that amount. Occurs in Brazil in syenite; near Popayan (Colombia) in alluvium, associated with chromite, iridium, palladium, gold, and copper; in the Urals in alluvium derived from crystalline rocks; and at Nijni-Tagilsk in serpentine along with chromite. It is also found in Borneo, California, and Carolina, and is said to have been found in the county of Wicklow in Ireland. The sands of many rivers yield it in small amount. Platinum does not occur in large masses. A mass in the Madrid Museum from Condoto weighs 26¾ oz.; masses have been found in the Urals from 11 to 21 lb.

Iron Platina is a sub-species. This, which has a composition FePt 2 , and contains from 11 to 13 per cent, of iron, is found at Nijni-Tagilsk. G. =14'6 to 15'8; H. =6. It is magnetipolar, and attracts iron much more strongly than an ordinary magnet.

27. Platiniridium.

In minute silver-white grains. H. =6 to 7; G. = 16'94 to 22'8. Contains 55'44 platinum, 27'79 iridium, 6'86 rhodium, 4 14 iron, 3'3 copper, '49 palladium. Is found in Brazil.

28. Iridium, Ir.

Cubic (fig. 27). H. = 6 to 7; G. = 21 '57 to 23'46. Cl. cubic, traces. Very slightly malleable. Silver-white to steel-grey. B.B. unchanged. Insoluble in all acids. C.c.: 76'8 iridium, 19'64 platinum, 0'89 palladium, 1'78 copper. Found at Nijni-Tagilsk, generally in minute grains. Is the heaviest known substance.

Avaite, sub-species. From Ava in India. C.c.: 60 iridium, 20 platinum (according to Pnnsep).

29. Palladium, Pd.

Cubic; in minute octahedrons, and in grains. H. = 4 '5 to 5; G. = 11'3 to 11'8. Malleable. Light steel-grey. B.B. infusible. Slowly dissolves in n. acid, forming a brown-red solution. C.c.: palladium, with a little platinum and iridium. From the gold sands of Brazil, often in small plumose crystalline lumps. Also from St Domingo, and the Urals. Does not tarnish with sulphurous fumes.

30. Allopalladium, Pd 3 .

Hexagonal; in small fiat hexagons. Cl basal, perfect. Lustre bright silvery. Colour pale steel-grey. From Tilkerode in the Harz, with gold.

31. Newjanskite (Osmiridiwn), Irθs (iridium 49'78, osmium 50'22) and Ir 3 Os.

Hexagonal; P 124°. 0P, P, ooP. Generally in flat scales. Cl. basal perfect. H. =7; G. =18'8 to 19'47. Lustre metallic. Colour tin-white. B. B. unchanged. Insoluble in all acids. The analyses of this mineral give quantities of iridium varying from 44 to 77 per cent., and of osmium from 21 to 49. Ruthenium, rhodium, and platinum make up the 100 parts. The largest quantity of ruthenium is 8 '49, and one variety from New Granada was found to contain no ruthenium, but 12'3 of rhodium, which is more than double its usual amount. Occurs with platinum in Choco (Colombia); at Newjansk and several localities in the Urals, in Australia, in northern California (somewhat abundantly in gold sands), also in Canada.

32. Sisserskite (Iridosmium), Ir0s 4 (iridium 19'9, osmium 80'1) and Irθs 3 (iridium 24 8, osmium 75'2).

Rhombohedral; R = 84° 28 ’. H. =7'5; G. = 21'12. Colour lead-grey to bluish. B.B. becomes black, with strong odour of osmic acid; in flame of spirit-lamp shines strongly, and colours flame yellowish red. Occurs in small quantity with newjanskite at all its localities, and in proportionally larger quantity at Sissersk in the Urals. It is used for pointing gold pens, and in the United States sells at 50 dollars an ounce.

COMPOUNDS OF FLUORINE, CHLORINE, BROMINE, AND IODINE (HALOID SALTS).

33. Fluorite (Fluor-spar), CaF.

Cubic (figs. 267 to 270, also figs. 31, 33, 36, 55, 56, 57, 58); also di vergent crystalline, granular, and compact. Cl. octahedral; fracture conchoidal; brittle. H. = 4; G. = 3 Ί to 3 '2. Transparent to pellucid. Lustre vitreous. Colourless, but generally coloured purple, blue, green, yellow, white, black, and pink. Sometimes two or three colours disposed in layers in one crystal. Frequently phosphoresces with different tints of light, when heated. B. B . decrepitates and fuses to an opaque bead. Sol. in s. acid with evolution of hydrofluoric acid. C.c.: 5Γ3 calcium, 48'7 fluorine. Common in veins, generally associated with metallic ores. Shetland, Sutherland, on the Avon, and Ballater in Scotland; Cumberland, Northumberland, Derbyshire, and Cornwall; Saxony, Bohemia, Freiberg. Used to be turned into vases and other ornaments ( ‘ ‘ blue John ”); formerly employed as a flux, now for etching and obscuring glass.

34. YTTROCERITE.

In crystalline crusts. H. = 4 to 5; G. =3'4 to3'5. Translucent; vitreous. Violet-blue to grey or white. B. B. infusible. Evolves fluorine when heated with sulphuric acid. C.c: fluorides of cerium, yttrium, and calcium. Finbo and Broddbo near Falun (Sweden), Massachusetts and New York.

35. Fluocerite, CeF + Ce 3 F 3 .

Hexagonal. H. = 4 to 5; G. = 4 '7. Opaque or translucent on the edges. Pale brick-red or yellowish; streak yellowish white. B. B. invisible. In closed tube gives out hydrofluoric acid. C.c.: 82'64 peroxide of cerium, 1'12 yttria, 16'24 hydrofluoric acid. Finbo and Broddbo.

36. Fluocerine, Ce 2 F s + (Ce 2 O 8 + H 2 O).

Massive; fracture conchoidal. H. =4'5 to 5. Opaque; resinous. Bright yellow to reddish brown; streak brownish yellow. B.B. infusible, darkens with the heat; colour restored on cooling. C.c.: cerium 17'6, fluorine 10'9. sesquioxide of cerium 66'4, water 5'1. From Finbo.

37. Bastnaesite, Ce 2 F 3 + Ce 2 O 3 + 4H 2 O, and

38. Hamartite, 2(LaO, CeO)3CO 2 + CeF 8 , are similar. The first is from Bastnaes in Sweden, the second from Pike’s Peak φ Colorado.

39. Fluellite, A1 2 F 3 .

Right prismatic. In acute rhombic octahedrons with truncated apex. Polaredges 109° 6'and 82° 12', middle 144°. H. =3. Lustre vitreous. Colour white; transparent. Stenna-gwyn in Cornwall.

40. Cryolite, 3NaF + Al 2 F 3 .

Anorthic; but mostly in cleavable masses. Μ: T 91° 57'; P: T 90° 2'; P·.M 90° 40'. Cl. P perfect, Μ and T imperfect; brittle. H. = 2 '5; G. = 2 '9 to 3 ’08. Vitreous, somewhat pearly on P. Translucent; after immersion in water transparent. Colourless and snow-white; but when deep-seated brown to black. Melts even in flame of candle to a white enamel. In open tube traces of hydrofluoric acid. Sol. in s. acid. C.c.: aluminium 13, sodium 32'8, fluorine 54‘2. Arksutfiord, Greenland; Miask, Siberia. Used for manufacture of a white glass, and extraction of aluminium.

41. Arksutite, (CaNa) 2 F +A1 2 F 3 . Ca :Na=l: 3.

Massive granular. H. = 2'5; G. =3'03 to 3 Ί 8. Cl. one distinct. Vitreous; white; translucent. C.c.: aluminium 18'6, sodium 23'3, calcium 6'8, fluorine 51 , 3. Arksutfiord.

42. Chiolite, 3NaF + 2Al 2 F 3 .

Pyramidal, and twins (fig. 272). Middle edge lll o 14'. Mostly granular. Cl. imperfect. H. = 4;G. =2’84 to 2'9. Resinous; white. Fuses more easily than cryolite; evolves hydrofluoric acid. C.c.: aluminium 18'6, sodium 23 - 4, fluorine 58. Ilmen Mts. near Miask.

43. Chodneffite, 2NaF + Al 2 F 3 .

G. — 3. Other characters like chiolite, and from same locality.

44. Pachnolite, 3(CaNa)F + Al 2 F 3 + 2H 2 O. Ca:Na = 3:2.

Oblique prismatic. ooP 98° 34'; always twins. Vitreous; white; semitransparent. C.c.: aluminium 12'3, calcium 16 ’ 1, sodium 12'4, fluorine 51'1, water 8Ί. Evolves water with crackling, when heated; other characters like cryolite, along with which it occurs in Greenland.

45. Thomsenolite, 2(CaNa)F + A1 2 F 3 +2H 2 O. Ca:Na=7:3.

Oblique prismatic. Prismatic planes striated; ∞P89° (fig. 273). Cl. basal, perfect. H. =2'5 to 4; G. =2'74 to 2 76. Vitreous; cleavage face pearly. White with yellow crust; translucent. C.c.: aluminium 15, calcium 15'4, sodium 7 '6, fluorine 52 '2, water 9'8. B. B. fuses more easily than cryolite to clear glass, decrepitating violently. Along with cryolite in Greenland.

46. Gearksutite, Ca 2 F + Al 2 F 3 + 4H 2 O.

Earthy. H. =2. White; dull; opaque. C.c.: aluminium 15'5, calcium 19'3, sodium 2'5, fluorine 41 '2, water 20 '3. Along with cryolite.

47. Evigtokite, 2CaF s + A1 2 F 6 + 2H 2 O.

Crystalline. Soft; brittle; like kaolin. C. c.: calcium 22'39, aluminium 16'23, sodium '43, fluorine 55'24, water 5 71. Arksutfiord, Green- f ⅛∙ 273 (sp. 45). land.

48, Prosopite.

Oblique prismatic. A hydrated silico-fluoride of aluminium and calcium. H. = 4; G. =2'89. Colourless imbedded crystals. From the tinmines of Altenberg.

49. Calomel, Hg a Cl.

Pyramidal; P 135 c 50' (fig. 274). H. =1 to 2; G. = 6 ’ 4to6'5. Translucent; adamantine. Yellowish white to grey. Sublimes unchanged in closed tube; with soda yields mercury. Insol. in n. acid. C.c.: mercury 85, chlorine 15. Moschellandsberg, Idria, Almaden.

50. Sylvite, KC1.

Cubic (figs. 26, 30); also massive. Cl. cubic.

H. =2; G=l'9 to 2. White or colourless. ’ .

Vitreous; soluble; taste like common salt. F1 ?' 2 ' 4 ∖ s P∙ 49 '' C.c.: potassium 52'5, chlorine 47'5. B.B. fuses, and colours flame violet. Crater of Vesuvius, and salt beds of Stassfurt.

51. Halite {Common Salt, Rock-salt), NaCl.

Cubic (fig. 21); generally granular, sometimes fibrous. Cl. cubic.

H. =2; G. =2'1 to 2'2. Transparent to translucent; vitreous. Colourless or white; but often coloured red, yellow, or blue. Taste saline. B.B. fuses and partly evaporates; colours flame yellow. C.c.: sodium 39'3, chlorine 60'7. In great beds at Wieliczka, Salzburg, Bex, &c., on the Continent; Cheshire in England. As an efflorescence in Brazil, Abyssinia, the Caspian and Aral Seas. As a sublimation among lavas at Vesuvius and other volcanoes.

52. Salmiac, NH 4 C1.

Cubic (figs. 30, 40, and 41 with 26, 33, 40). Cl. octahedral; also stalactitic, globular, and as an efflorescence. H. = 1 '5 to 2; G. = 1 '5 to 1 '6. Pellucid; vitreous. Colourless, but sometimes stained. Taste pungent. B.B. directly volatile; in copper colours flame blue-green. C.c.: 32 ammonia, 66'4 chlorine. A sublimate on active volcanoes. Vesuvius, island of Volcano, Iceland. Near coal-seams which have taken fire, in Scotland and at Newcastle.

53. Chloro-Calcite, CaCl + (KCl, NaCl).

Cubic. Vesuvian bombs.

54. Cerargyrite, AgCl.

Cubic (fig. 26). Twins on octahedral face. No cl.; chiefly massive in crusts. H. =1 to 1'5; G. =5'5 to 5’6. Fracture conchoidal. Malleable. Translucent; adamantine to resinous. Grey, yellowish, and greenish. B.B. fuses easily to a dark bead, reduced in inner flame. Soluble in ammonia. C.c.: silver 75, chlorine 25. Johann-Georgenstadt, Mexico, Peru.

55. Embolite, 2AgBr + 3AgCl.

Cubic (fig. 29); also massive or concretionary. H. = 1 to 1 , 5; G. = 5'8. Adamantine to resinous. Green and yellowish green. C.c.: silver 67, chlorine 13, bromine 20. Chili, Mexico, Honduras.

56. Bromite, AgBr.

Cubic (figs. 26, 30). H. = 1 to 2; G. =5'8 to 6. Splendent. Yellow to olive-green; streak siskin-green. B.B. fusible easily. C.c.: silver 57‘5, bromine 42 ’ 5. San Onofre and Plateros (Mexico).

57. Iodite, Agi.

Hexagonal. Cl. basal; also massive, and in crystalline plates some inches in width; these are flexible. H. = 1 to 1 '5; G. = 5'5to 5'7. Translucent; adamantine. Citron and sulphur-yellow; streak yellow. B.B. fusible, colours the flame purple-red, and leaves button of silver. C.c.: silver 46, iodine 54. Zacatecas in Mexico, Algodones in Chili, Arizona, rarely in Spain.

58. Coccinite, Hgl 2 .

In grains of an adamantine lustre, from Casas-Viejas in Mexico. Colour red to yellow; in acute rhombic prisms. Also from Zimapan and Culebras.

59. Tocornaclite, Agi + Hg 2 I.

Amorphous, yellow, soft. Chanarcillo in Chili.

60. Cotunnite, PbCl.

Right prismatic. H. = 2; G. = 5'238. Transparent; high adamantine to pearly. White. C.c.: lead 74, chlorine 26. Crater of Vesuvius.

61. Molysite, Fe 2 Cl 3 .

Incrusting. Brownish red and yellow. On lavas of Vesuvius. C.c.: iron 34'5, chlorine 65'5.

62. Carnallite, KCl + 2MgCl + 12H 2 O.

Right prismatic. Noel. Conchoidal fracture. H. =2 to 2'5; G. = 1'6. Colourless, generally red from iron. C.c.: 34 ’ 2 chloride of magnesium, 26'9 chloride of potassium, 38'9 water. Stassfurt, Galicia, Persia.

63. Tachhydrite, CaCl + 2MgCl + 12H 2 O.

Massive. Yellow, translucent, very deliquescent. In anhydrite. C.c.: calcium 7'46, magnesium 9'51, chlorine 40'34, water 42'69. Stassfurt.

64. Kremersite, KCl + NH 4 Cl + Fe 2 Cl 3 +3H 2 O.

Cubic; in octahedra. Ruby-red. Soluble. Fumaroles of Vesuvius.

65. Erithrosiderite, 2KC1 + Fe 2 Cl 3 + 2H 2 O.

Right prismatic. Vesuvian lava.

66. Matlockite, PbCl + PbO.

Pyramidal; P 136° 17'. Crystals tabular. Cl. basal; fracture conchoidal. H. =2'5; G. =7'21. Translucent; adamantine. Yellowish white. B. B. fuses easily with decrepitation; colours flame blue. C.c.: chloride of lead 55'5, oxide of lead 44'5. Cromford in Derbyshire.

67. Mendipite, PbCl + 2PbO.

Right prismatic; chiefly massive. Cl. ∞P perfect 102° 36'. H. = 2'5 to 3; G. = 7'to 7'1. Fracture conchoidal. Translucent; adamantine to pearly. Yellowish or greyish white. BB. decrepitates, fuses easily. Sol. in n. acid. C.c.: chloride of lead 40, protoxide of lead 60. Mendip Hills, and Brilon in Westphalia.

68. Schwartzembergite, PbI + 2PbO.

Rhombohedral; in thin crusts. H. =2 to 2*5; G. =57 to 6*3. Adamantine. Honey-yellow. Desert of Atacama.

69. Atacamite, CuC1 + 3CuO,H 2 O .

Right prismatic; ooP (Jf) 112 β 25', P ∞ (P) 106° 10', οοϊ>οο (Ä) (fig. 275); also reniform. Cl. h perfect. Semitransparent; vitreous.

Emerald - green; streak applegreen. B. B. fuses, leaving copper. Easily soluble in acids. C.c.: copper protoxide 55'85, copper 14*86, chlorine 16*61, water 12*68. Atacama, Chili; Tarapaca, Peru; Bolivia; Burra-Burra, Australia; Serra de Bembe, Ambriz, Africa; Vesuvius and (?) Etna.

70. Tallingite, CuCl, H 2 O + 4CuO, H 2 O.

In crusts. H. =3; G. =3*5. Bright blue to greenish blue. Translucent; brittle. Botallack in Cornwall.

71. Percylite, (PbCl + PbO) + (CuCl + CuO).

Cubic (com. of figs. 26, 30, 33, 36). H.-2. Vitreous. Sky-blue. Sonora in Mexico.

_. 97ft . 72. Connellite. g, z70 < 8p * 72 '∙ Hexagonal (fig. 276). b :r 143° 10'; r: r 132° 50'. Crystals acicular. Vitreous; translucent. Vitriol-blue. A chloride and sulphide of copper. Wheal Unity and Wheal Damsel (Cornwall).

OXIDES OF METALS.

1. Suboxides and Protoxides.

73. Cuprite, Cu 2 O .

Cubic (figs. 22, 30, 33, 26, with 39, 40). Compact and granular. Cl. octahedral; brittle. H. = 3*5 to 4; G. =57 to 6. Transparent and opaque; adamantine. When transparent, crimson; when opaque, cochineal or brick-red. Often tarnished grey. B. B. becomes black, fuses, and is reduced on charcoal. Soluble in acids and in ammonia. C.c.: 88'9 copper, 11*1 oxygen. Cornwall, Siberia, Banat, Chessy near Lyons, Linares in Spain, Urals, South Africa, Burra-Burra. Valuable copper ore. Chalcotrichite consists of cubes elongated so as to become fibrous. Tile-ore is a ferruginous variety. Hepatic copper, liver ore, or pitchy copper ore seems to be a product of the decomposition of chalcopyrite. Delafossite, Cu 2 O + Fe 2 O 3 , from Bohemia and Siberia.

74. Water, H 2 O .

Hexagonal, when solid, in complex twins in snow crystals; rhombohedric by cleavage, in ice. H. = 1 *5; G. = ∙918. Hence 1000 of water—1089 *5 of ice, or water expands τ 1 r th in freezing. Transparent; vitreous. Colourless, but in bulk pale emerald-green. R 117° 23". Cl. basal. Water when pure colourless, in mass bluish green. Occurs in centre of geodes of chalcedony in China; of druses of quartz in California and many other countries; in zeolitic cavities to the amount of several gallons in the Faroes, also in the Hebrides, &c. Water of the ocean, from holding saline matters in solution, has G. = 1Ό27 to 1Ό285. Waters of saline lakes contain sometimes 26 per cent, of salts, and have G. 1*212. Besides its vast bulk in the ocean, water occurs in enormous amount in the solid form, often as water of crystallization in rocks and minerals, e.g., zeolites. Igneous rocks in some districts are converted largely into saponite, which contains 25 per cent, of water. Water is the standard for specific gravities of solids and liquids; 1 cubic inch at 60° F. and 30 inches of the barometer weighs 252*458 grains ∙. 1 litre weighs 1000 grammes.

75. Periclase, MgO.

Cubic; in cubes and octahedrons. Cl. do. H. =6; G. =3*6 to 375. Transparent; vitreous. Grey to dark green. B.B. infusible. Sol. in acids. C.c.: magnesia, with 6 to 8 of iron oxide. Somma.

76. Bunsenite, NiO .

Cubic; in octahedrons., H. - 5 *5: G. - 6 *4. Vitreous. Pistachiogreen. Johann-Georgenstadt.

77. Zincite, ZnO.

Hexagonal and granular. Cl. basal. H. =4 to 4*5; G. = 5*4 to 5*5. Adamantine; translucent. Blood-or hyacinth-red; streak orange-yellow. B. B. infusible, but phosphoresces. C.c.: zinc 80*26, oxygen 1974; sometimes with manganese peroxide. Valuable ore of zinc. Franklin and Sterling in New Jersey.

78. Massicot, PbO.

Massive; scaly crystalline. H. — 2; G. —7*8 to 8. Sulphur-or lemon-yellow; often contains iron. Popocatepetl in Mexico.

79. Melaconite, CuO .

Cubic; compact. H. =3 to 4; G. = 6 to 6*3. Black. Β.Β. infusible; soluble in acids. Cornwall, Leadhills, Lake Superior, Burra-Burra.

80. Tenorite, CuO.

Oblique prismatic; occurs in thin scales of metallic lustre on lava of Vesuvius. Colour black and dark-red.

2. Sesquioxides.

81. Corundum, A1 2 O 3 .

Hexagonal; R 86° 4'. Twins common. Cl. rhombohedral, and basal. Excessively tough, and difficultly frangible. H. = 9; G. — 3 *9 to 4*2. Transparent or translucent; vitreous, but pearly to metallic on basal face. B. B. unchanged. As Corundum, white, grey, and greenish, frequently with bronzy lustre on basal face. C.c.: alumina, with a little peroxide of iron. China, Ceylon, Bohemia, Malabar, Macon in North Carolina (one crystal 300 lb weight). Emery is compact, crystalline, granular; grey to indigo-blue. Asia Minor, Naxos, Spain, Greenland, America. Corundum is used when crushed for cutting and polishing gems in China and India, emery in powder for grinding. Alumina occurs also in a purer state in transparent crystals of various tints of colour. When red and of the colour of pigeon’s blood they are termed Rubies ; these come from Syriam in Pegu, Ava, Ceylon, Bohemia, and near Expailly. When 5 carats in weight a ruby is twice the value of a diamond of the same size, when 10 carats three times the value.

When blue the crystal is the Sapphire, found chiefly in Ceylon and Pegu; when green it is the Oriental Emerald, when yellow the Oriental Topaz, when purple the Oriental Amethyst,— the adjective here distinguishing them from the true or occidental stones of the same name. Other tints of colour also occur, but with the exception of the red and blue they are seldom pure or deep. The prism when cut with a hemispherical dome sometimes displays a six-rayed star, either of a bright gold or a silvery white colour, upon a greyish blue ground. These receive the name of Asteria Sapphires. The same crystal frequently shows portions of even three different tints. When perfectly devoid of colour, they are called Water Sapphires·, such are little inferior to the diamond in brilliancy, but do not disperse rays of light to the same extent.

82. Haematite, Fe 2 O 3 .

Hexagonal and rhombohedral; R 86°. Crystals rhombohedric, prismatic, and tabular. Twins with axes parallel. Cl. R, and basal; fracture conchoidal; brittle. H. =5*5 to 6*5; G. =5*1 to 5*3. Opaque, but in thin laminae transparent and blood-red. Brilliant metallic lustre, iron-black to steel-grey, often brilliantly tarnished of red, yellow, green, and blue tints; streak cherry-red. B. B. in the inner flame becomes black and magnetic. Sol. in acids. C.c.: iron 70, oxygen 30. The following are varieties or subdivisions:—

Elba Iron Ore, highly modified rhombohedral crystals, often brilliantly tarnished. Specular Iron Ore, in thin flat crystals, often from volcanoes, as on the island of Ascension; this variety includes Micaceous Iron, thin, lamellar, and curved, and Red Iron Froth, scaly. Red Haematite, in botryoidal and stalactitic forms, which are internally composed of radiating fibres, and often have a concentric structure; the external surface has a dark red to a brownish red hue. Compact and Ochrey varieties, with more or less aluminous impurity, pass into Reddle or red chalk, and when still more earthy into jaspery and columnar ores. This ore is very commonly distributed:—micaceous iron at Pitfichie in Aberdeen and Birnam in Perthshire; red haematite at LeadΛlls and at Ulverston in Lancashire; specular iron at Tavistock in Devonshire and in Cumberland. Martite seems to be the same substance in pseudomorphs after magnetite; it occurs in octahedra in Bute, Framont (Vosges), New York, and Brazil.

83. Ilmenite, (Fe,Ti) 2 O 3 .

Rhombohedral; R 86°. Crystals rhombohedral and tabular, also in twins. Cl. basal; fracture conchoidal. H. = 5 to 6; G. = 4 ’ 66 to 5. Opaque, semimetallic, iron-black to dark brown; streak black or reddish brown. Sometimes slightly magnetic. B.B. infusible, but with microcosmic salt forms a red glass. Slowly sol. in s. acid when powdered. C. c.: peroxide of iron, with from 8 to 53 per cent, oxide of titanium. Occurs in metamorphic rocks. Common in chloritic gneiss in Scotland; Menaccan (Cornwall), Ilmen Mountains, Salzburg, Egersund (Norway), Arendal, Dauphiné {Crichtonite), Massachusetts (Washingtonite).

84. Iserine.

Cubic; in octahedra. Strongly magnetic; in other respects similar to ilmenite, but occurs in igneous rocks. Common as black ironsand in Scotland; Iserweise in Bohemia, Auvergne, Canada, New Zealand.

3. Compounds of Sesquioxides with Protoxides (Spinels).

85. Magnetite, FeO, Fe 2 O 3 .

Cubic (figs. 35, 30, 33, 29, 34, 37, with 40, 41, 36). Hemitropes common on octahedral face (fig. 169). Twins (fig. 261). Faces of oo0 striated in long diagonal. Often compact and granular. Cl. octahedral; fracture conchoidal or uneven; brittle. H. = 5 '5 to 6 '5; G = 4 - 9 to 5 ’ 2. Opaque; lustre metallic. Iron-black to brown; streak black. Highly magnetic; often polar, forming natural magnets. B.B. becomes brown and non-magnetic, fusing with difficulty. Powder sol. in h. acid. C.c.: 31 protoxide and 69 peroxide of iron; or 72 - 4 iron, 27’6 oxygen; sometimes with titanic acid. In crystals in Shetland and Sutherland; also Cornwall and Antrim, Traversella (Piedmont), Tyrol, Styria. Massive at Dannemora and Taberg (Sweden), Norway, Urals, Harz, Saxony, Elba. This is the most important ore in Norway, Sweden, and Russia, and affords the finest iron.

86. Magnesio-Ferrite, MgO, Fe 2 O 3 .

Cubic (fig. 30). H.=6 to 6*5; G.=4∙57 to 4'66. Other characters same as magnetite. C.c.: magnesia 20, peroxide of iron 87. Fumaroles of Vesuvius.

87. Jacobsite, (MnO, MgO), (Fe 2 O 3 , Mn 2 O 3 ).

Cubic; 0. Black; vitreous; streak red. Nordmark in Sweden. 88. Franklinite, (FeO, ZnO, MnO), (Fe 2 O 3 , Mn 2 O 3 ).

Cubic (figs. 34, 64); also granular. Cl. octahedral; fracture conchoidal; brittle. H. =55 to 6 ’ 5; G. =5 ’ 07. Metallic lustre. Iron-black; streak reddish brown. Opaque; slightly magnetic. B. B. infusible, but shines and throws out sparks. On charcoal with soda a deposit of oxide of zinc. Sol. in h. acid with evolution of chlorine. C.c.: about 67 iron oxide, 17 manganese peroxide, 16 zinc oxide. Franklin and Sterling (New Jersey).

89. Chromite, FeO, Cr 2 O 3 .

Cubic; in octahedra, generally granular-massive. H. =5‘5; G. =4 , 4to4 - 5. Opaque; semimetallic to resinous. Iron-black to dark brown; streak reddish brown. Fracture uneven; sometimes magnetic. B. B. unchanged; in red. flame becomes magnetic; with borax forms an emerald-green bead. Not soluble in acids. C.c.: 19 to 37 protoxide of iron, 0 to 15 magnesia, 36 to 64 peroxide of chromium, 9 to 21 alumina. Unst (Shetland), Towanrieff (Aberdeenshire), Silesia, Bohemia, Styria, Urals, Turkey, Baltimore, Massachusetts, and Hoboken. The ore of chromium; used for dyes. Irite is chromite mixed with iridosmium.

90. Uraninite {Pitch Blende), UO, U 2 O 3 .

Cubic (fig. 30); usually massive and botryoidal. H. = 5 to 6; G=6 ∙5 to 8. Lustre pitch-like to submetallic. Colour velvet-black, brownish black, and grey. B.B. infusible. Not sol. in h. acid, but easily in hot n. acid. C.c.: oxides of uranium 80, with a mixture of other oxides. Johann-Georgenstadt, Annaberg, Przibram, Redruth in Cornwall. The chief ore of uranium.

91. Gahnite, ZnO, A1 2 O 3 .

Cubic (figs. 166, 30, 33, and with 39, 40). Hemitropes like magnetite. Cl. O; brittle, with conchoidal fracture. H. =7 ’ 5to 8; G. = 4 ’ 3 to 4 - 9. Opaque; vitreous to resinous. Dark leek-green to blue; streak grey. B.B. unchanged. Unaffected by acids or π⅛ es ' · θ' c * i oxide of zinc, 56 alumina. Falun, Broddbo, Haddam in Connecticut, and Franklin in New Jersey. Dysluite contains 42 per cent, sesquioxide of iron; and Kreittonite contains 24 oxide of manganese.

92. Hercynite, FeO, A1 2 O 3 .

Cubic; generally granular massive. H. = 7 '5 to 8; G. = 3 9 to 3 - 95. B.B. infusible. C.c.: oxide of iron 41*1, alumina 58 ’ 9. Ronsberg in the Böhmerwald.

93. Spinel, MgO, A1 2 O 3 .

Cubic (figs. 30, 33, 40 with 26); hemitropes united by face of O. Cl. octahedral; fracture conchoidal. H. =8; G. = 3 - 4 to 4Ί. Transparent to opaque; vitreous. Black, red, blue, green; streak white. B.B. infusible and unchanged. C.c.: 28 magnesia, 72 alumina; some with a little iron, and the red varieties some chromium. Varieties are— Spinel Ruby when scarlet, Balas Ruby when rose-red; both often sold as the true ruby, but not nearly so valuable; when of 4 carats valued at half the price of a diamond the same size. These come from Pegu (native name Balachan). The violet-coloured is the Alabandine ruby from Alabandin in Caria, (AsiaMinor). The orange red is the Rubicella. The above also occur at Ceylon, Ava, and Siam. Sapphirine is pale sapphire-blue to greenish or reddish blue; from Aker in Sweden, Greenland, and North America. Pleonaste, dark green or blue to black; from Candy in Ceylon. Chlorospinel, grass-green with a yellowish white streak; from Zlatoust. Water-spinel colourless; from Ceylox. Picotite is a dark blue chromiferous variety from serpentine.

94. Chrysoberyl, GIO, A1 2 O 3 .

Right prismatic (fig. 284). Twins common, united by a face of Pα> (fig. 285, also 156). Cl. brachydiagonal imperfect, macrodiagonal more so; fracture conchoidal. H. = 8 ’ 5; G. = 3 - 68 to 3’8. Transparent or translucent; vitreous. Greenish white, leek-green, and dark emeraldgreen. B.B. infusible. Not affected by acids. C.c.: glucina20, alumina 80. Brazil, Ceylon, India, the Urals, Haddam in Connecticut. A very valuable gem. It sometimes possesses an opalescent band, which when the stone is cut en cabochon appears as a streak of floating light; whence it derives its name of Cymophane. It is then also called the chatoyant or Oriental chrysolite, and when fine is of extreme value. The emerald-green variety, or Alexandrite, is columbine-red by transmitted light.

4. Deutoxides.

95. Rutile, TiO 2 .

Pyramidal; prisms dominant. P 84 40'; Poo 65° 35' (figs. 286, 287). Hemitropes common, with axes of halves 114° 26'. Cl. 00 P and 00P00, perfect. H. =6 to 6’5; G. = 4 ’ 2 to 4 ’ 3. Transparent to opaque; adamantine lustre. Brown-red, red, pale yellow, and black; streak yellowish brown. B. B. unchanged; with borax in the ox. flame forms a greenish, in the red. flame a violet glass. Not affected by acids. C. c.: titanic acid, with some peroxide of iron. Craig-cailleach and Ben-y-Gloe (Perthshire), The Cobbler and Ben-Bheula (Argyllshire), Alps, Limoges, Norway, Brazil. Large crystals at Titanium Mount (Lincoln county, Georgia). Used in porcelain painting, and for tinting artificial teeth. When attenuated crystals are imbedded in rock-crystal they are called Venus’ hair.

96. Anatase, TiO 2 .

Pyramidal; pyramids dominant. P 136° 36' (fig. 288). Cl. basal, and P, both perfect; brittle.

H. - 5 ∙5 to 6; G. - 3 ∙8 to 3 93. Transparent to opaque; lustre adamantine to metallic. Indigo-blue, yellow, brown, rarely colourless; streak white. B. B. infusible. Sol. in hot s. acid. C.c.: titanic acid, with a little iron and rarely tin. Cornwall and Devonshire, the Alps, Dauphine, Valais, the Urals, Minas Geraes (Brazil).

97. Brookite, TiO 2 .

Right prismatic; with polar edges 135° 37' and 101° 3' (fig. 289). Cl. macrodiagonal. H. - 5 ’5 to 6; G. = 3'86 to 4'2. Transparent to opaque; lustre metallic adamantine. Yellowish, reddish, and hair-brown; streak yellowish white to white. B.B. infusible; with microcosmic salt, a brownish yellow glass. C.c.: titanic acid, with 1 to 4’5 per cent, peroxide of iron. Snowdon and Tremadoc (Wales), Chamouni, Bourg d’Oisans, Miask. Arkansitc is iron-black, and submetallic, in thick crystals from Arkansas, U.S.

98. Cassiterite, SnO 2 .

Pyramidal. P 87° 7'; P∞ 67° 50' (figs. 290 to 292). Crystals ∞P, P; or ooP (<∕), P (s), ooPoo(Z); or with Poo (P), (fig. 290); and also ooP2 (r), and 3P$ (z), (fig. 291). Hemitropes very common, combined by a face of Poo with the chief axes 112° 10' (figs. 293,171,172, 173); also fibrous (Wood Tin), or in rounded fragments and grains (Stream Tin). Cl. prismatic along ooP, andooP∞, imperfect; brittle. H. =6 to 7;

G. =6’8 to 7. Translucent or opaque; adamantine or resinous. White, but usually grey, yellow, red, brown, and black; streak white, light grey, or brown. B.B. in the forceps infusible; on charcoal, in the inner flame, reduced to tin. Not affected by acids. C.c.: 78 ∙6 tin and 2Γ4 oxygen, but often mixed with peroxide of iron, or manganese, or tantalic acid. Cornwall, Bohemia, Saxony, also Silesia, Haute-Vienne in France, Greenland, Russia, North and South America, Malacca, Banca, and Queensland. Almost the only ore of tin.

99. Hausmannite, 2MnO, MnO 2 .

Pyramidal. P 116° 59'; Poo 98° 32'(fig. 110). Twins common, and rosettes of twins (figs. 174,175). Cl. basal, perfect, less so P and Pco; fracture uneven. H. =5’5; G. ≈=47 to 4’8. Opaque; metallic lustre. Iron-black; streak brown. B.B. infusible, but becomes brown. Sol. in h. acid, with evolution of chlorine. Powder colours s. acid red. C.c.: 31 protoxide and 69 peroxide of manganese. Ihlefeld and Ilmenau in the Harz, and Sweden.

100. Braunite, MnO, MnO 2 . ·

Tetragonal. P 108° 39'. Cl. P; brittle. H. - 6 to 6 ’5; G. - 4 Ί to 4'9. Metallic lustre. Colour and streak dark brownish black. C.c.: 70 manganese and 30 oxygen, generally with about 8 per cent, of silica. Ihlefeld and St Marcel. Marceline has violet tarnish.

101. Pyrolusite, MnO a .

Right prismatic; ooP93 β 40'j generally radiating fibrous, or compact earthy. Cl. ooP; friable. H. = 2 to 2 5;

G. = 4 - 7 to 5. Opaque; lustre silky to semi-metallic. Dark steel-grey to black; streak black. Soils. B. B. infusible, loses oxygen and becomes brown. Sol. in h. acid, with evolution of chlorine. C.c.: manganese 63, oxygen 37. Arndilly (Banffshire), Cornwall and Devon, Ilmenau, Ihlefeld, France, Hungary, Brazil. Used for removing the green iron tint from glass; hence its name and that of Savon de verrier. Also for obtaining oxygen and chlorine. Varvicite is a variety with 5 per cent, of water, from Warwickshire.

102. Crednerite, 3CuO, 2(MnO,MnO 2 ).

Oblique. H. — 4 - 5; G = 5. Metallic. Black; streak brown. Thuringia.

103. Plattnerite, PbO 2 .

Hexagonal. ooP120°. Cl. indistinct; brittle. G.-94. Opaque; metallic. Iron-black; streak brown. C.c.: lead 86’2, oxygen 13 ·8. Leadhills.

104. Minium, 2PbO, PbO 2

Pulverulent. H. = 2 to 3; G. = 4 ’ 6. Dull. Colour bright red; streak orange-yellow. B.B. fuses easily and reduced. Sol. in h. acid. C.c.: lead 907, oxygen 9’3. Leadhills, Weardale in Yorkshire, Anglesea, Badenweiler, Siberia.

5. Hydrous Oxides.

105. Sassoline, B 2 O 3 , H 2 O.

Anorthic. 0P: oofoo 75° 30'. Scaly six-sided plates. Cl. basal. Flexible and sectile. H. — 1; G. — 14 to 1 '5. Translucent; pearly; white; taste bitter; greasy. Sol. in hot water. C.c.: boracic acid 5645, water 43’55. Hot springs of Sasso, near Siena, Tuscany; and with sulphur in the crater of Volcano, Lipari Islands.

106. Turgite, 2Fe 2 O 3 + H 2 O .

Massive and fibrous, also earthy. H. = 5 to 6; G. =3’54 to 4’68. Lustre satin-like, also dull. Colour reddish black to bright red. Botryoidal surfaces lustrous like limonite.

Opaque. C.c.: iron sesquioxide 947, water 5’3. B.B. decrepitates violently and yields water. Kerrera (Hebrides), Bogoslovsk (Urals), and many limonite localities. Frequently taken for limonite.

107. Diaspore, A1 2 O 3 , H 2 O.

Right prismatic; ∞P129°47'j usually thin foliated. Cl. brachydiagonal, perfect; brittle. H. =6;G. =3’3 to 3’4. Vitreous; pearly on cleavage-planes. Colourless to yellowish, greenish, or violet. B.B. infusible, decrepitates. Insoluble. C.c.: alumina 85, water 15. Schemnitz, Broddbo, Switzerland, Naxos, Chester, Massa chusetts. Fig. 295.

108. Göthite, Fe 2 O 3 , H 2 O.

Right prismatic; ooP 94° 53'; also columnar, fibrous, or scaly. Cl. brachydiagonal, perfect; brittle. H. =5 to5’5; G.=3∙8 to4∙4. Opaque; or fine crystals transparent, and hyacinth-red; lustre adamantine or silky. Colour yellow, red, or dark brown; streak brownish yellow. B.B. becomes magnetic, difficultly fusible. Sol. in h. acid. C.c.: peroxide of iron 90, water 10. Hoy (Orkney), Achavarasdale (Caithness), Salisbury Crags (Edinburgh), Lostwithiel, Clifton, Bristol, Przibram, Siegen, Saxony. Urals, North America.

109. Manganite, Mn 2 O 3 , H 2 O.

Right prismatic, sometimes hemihedric; α>P ( J∕) 99 ’ 40. Crystals prismatic (figs. 298 to 300); vertically striated; also columnar or fibrous. Hemitropes common. Cl. brachydiagonal, perfect; brittle.

H.-3∙5 to 4; G.=4∙3 to 44. Opaque; metallic lustre. Steel-grey to iron-black; streak brown. B.B. infusible. Sol. in warm h. acid. C.c.: peroxide of manganese 89’9, water 10 ’ l. Grandholm (Aberdeenshire), Cork, Upton Pyne (Exeter), Churchhill (Somerset), Warwickshire, Ihlefeld, Thuringia, Norway, Sweden, Nova Scotia.

110. Limonite, 2Fe a O 3 + 3H 2 O.

Fibrous, botryoidal, and stalactitic, sometimes earthy. H. =4’5 to 5’5; G. =3’4 to 3’95. Opaque; lustre silky, glimmering, or dull. Brown, yellowish and blackish brown, often black on surface; streak ochreyellow. In closed tube yields water and becomes red. B.B. in inner flame becomes magnetic, fusing to a glass. C. c.: peroxide of iron 85’6, water 14’4. Sandlodge (Shetland), Hoy (Orkney), Clifton, Bristol, Cornwall, Harz, Thuringia, Nassau, Styria, Carinthia, Siberia, United States.

111. Xanthosiderite, Fe 2 O 3 ,2H 2 O.

Fibrous, stellate, also as an ochre. H. = 2 '5. Silky or greasy, pitch-like or earthy. In needles, golden-yellow or brown-red; as an ochre, yellow, red, or brown; streak ochre-yellow. B. B. like limonite. C.c.: peroxide of iron 81’6, water 18’4. Hoy (Orkney), Achavarasdale, Kilbride, Wicklow, Ilmenau, Goslar, and Elbingerode in the Harz.

112. Βεαίχιτε, (3A1 2 O 3 , Γe 2 O 3 ), 2H 2 O.

Oolitic, concretionary, disseminated; also earthy and clay-like. G. =2’55. White, grey, ochre-yellow, brown, and red. C.c.: alumina 50 ’4, peroxide of iron 26 Ί, water 23 5. From Beaux (or Baux) near Arles, and elsewhere in France. In grains in compact limestone. Pure varieties used for manufacture of aluminium.

113. Eliasite, U 2 O 3 + 2H 2 O.

Amorphous masses; resin-like. H. = 3 ’ 5 to 4'5; G. = 4 to 5. Reddish brown to black; streak wax-yellow to olive-green. C. c.: 68’5 per cent, sesquioxide of uranium. 10 of water, with impurities. Elias mine (near Joachimsthal).

114. Brucite, MgO,H 2 O.

Rhombohedral; R 82° 22'; also foliated and botryoidal columnar. Cl. basal, perfect; sectile; laminae flexible. H. = 2; G. =2’3 to 2’4. Translucent, pearly. Colourless. B.B. infusible. Easily soluble in acids. C. c.: 69 magnesia, 31 water. Nemalite is a fibrous variety with silky lustre. Swinaness and Quin Gio in Unst, Beresovsk in the Urals, Hoboken, New Jersey, Texas, Pennsylvania.

115. Pyrochroite, MnO, H 2 O.

Foliated. H. =2’5. Pearly, white, but changing through bronze to black. Flesh-red by transmitted light. In matrass becomes verdigris-green, finally black, yielding water. Sol. in h. acid. C.c.: protoxide of manganese 79’8, water 20'2. In veins in magnetite at Paisberg in Sweden.

116. Gibbsite (Hydrargillite), A1 2 O 3 , 3H 2 O.

Hexagonal. C.c.: 65'5 alumina, 34’5 water. The crystals are from Zlatoust in the Urals; stalactites from Richmond in Massachusetts and Villa Rica in Brazil.

117. Limnite, Fe 2 O 3 , 3H 2 O∙

Massive in stalactites, also as a yellow ochre. Like limonite, but pitchy lustre. C.c.: peroxide of iron 74 ’ 8, water 25’2. Leadhills, Botallack (Cornwall), Novgorod (Russia).

118. Hydrotalcite, A1 2 O 3 , 3H 2 O + 6MgO, H 2 O + 6H 2 O.

Hexagonal. Cl. basal, foliated, and somewhat fibrous. H. = 2; G. = 2’04. White, pearly. Greasy to the touch. Translucent. C.c.: alumina 16’8, magnesia 39’2, water 44. Zlatoust, Urals; Suarum, Norway; New York.

119. Pyroaurite, Fe 2 O 3 , 3H 2 O + 6MgO, H 2 O + 6H 2 O.

Hexagonal; tables and scaly coatings. Lustre pearly to submetallic. Colour white to gold-yellow. Translucent. B.B. infusible, yields water. Sol. in h. acid. C.c.: peroxide of iron 23’9, magnesia 35’8, water 40’3. HaafGrunay in Shetland, Lângban in Wermland.

120. Gummite, U 2 O 3 , 3H 2 O .

In rounded lumps, resembling gum. H. =2’5 to 3; G. =3’9 to 4’2. Lustre greasy. Reddish yellow to yellowish brown. C.c.: 72 per cent, sesquioxide of uranium water 14’75, with impurities. J ohann -Georgenstadt.

121. Psilomelane, (BaO, MnO) MnO 2 + 3H 2 O, MnO 2 + 3H 2 O.

Massive and botryoidal; fracture conchoidal. H. = 5’5 to 6; G. = 4Ί to 4’3. Bluish black. B.B. infusible. About 80 per cent, of oxide of manganese, with baryta, potash, and water. Hoy (Orkney), Leadhills, Cornwall, Devon, Schneeberg, Ilmenau, Vermont in France. Wad is similar, but sometimes soft and light. Leadhills, Cornwall, Haτz, France.

122. Chalcophanite, MnOZnO + 2MnO 2 + 2H 2 O.

Hexagonal. R: R 114° 30'. Cl. basal. H. =2’5; G.—3'91. Metallic lustre. Blue-black; streak brown, dull. Opaque; flexible. C.c.: manganese binoxide 59’94, protoxide 6’6, zinc oxide 21’7, water 11’6. Sterling Hill (New Jersey).

OXIDES OF NON-METALS.

1. Oxides of Arsenic-Antimon y Family (Teroxides).

123. Arsenolite, AsO 3 .

Cubic; in octahedra; also botryoidal, stalactitic. H. =1’5; G. = 3’7. Lustre vitreous. White; streak pale yellow. Translucent Sublimes inclosed tube, condensing in brilliant octahedra. C.c.: arsenic 75’76, oxygen 24’24. Cornwall, Andreasberg, Joachimsthal. Kapnik (Hungary), Nevada, California.

124. Senarmontite, SbO 3 .

Cubic; in octahedrons. Cl. octahedral, also massive granular. H. = 2 to 2 ’5; G. = 5 ’22 to 5 '3. Transparent; adamantine. White or grey. B.B. in inner flame fuses and colours the flame greenish blue. Sol. in h. acid. C.c.: antimony 83’56, oxygen 16’44. Endellion in Cornwall, Constantine in Algeria, Malaczka in Hungary.

125. Valentineite, SbO 3 .

Right prismatic; ooP137°. Cl. ooP, perfect. H. =2’5 to 3; G. =5’5 to 5’6. Translucent; adamantine to pearly. Yellowish white, browngrey; streak white. Other properties and composition like senarmontite. Glendinning (Dumfriesshire), Przibram, Braunsdorf (Saxony), Harz, Hungary, Allemont (Dauphine), Siberia.

126. Bismite, BiO 3 .

Massive, earthy. G. = 4’36. Grey, yellow, green. C.c.: bismuth 89’65, oxygen 10’35. St Agnes (Cornwall), Schneeberg, Siberia.

127. Molybdite, MoO 3 .

Right prismatic; α>P136°48'. In capillary crystals, also powdery. H. = 1 to 2; G. =4’5. Straw-yellow to yellowish white. C.c.: molybdenum 65’71, oxygen 34’29. With molybdenite at many of its localities.

128. Tungstite, WO 3 .

Earthy. Soft yellow or yellowish green. Sol. in alkalies. C.c.: tungsten 79’3, oxygen 20’7. Cumberland and Cornwall, Monroe in Connecticut.

129. Cervantite, SbO 3 + SbO δ .

Right prismatic. Acicular, generally earthy. H. = 4 to 5; G. = 4 Ί. Isabel-yellow, reddish white. B. B. on charcoal reduced; unaltered per se. Sol. in h. acid. Harehill, Ayrshire; Endellion, &c., Cornwall; Cervantes, Spain; Felsöbanya, Hungary; Mexico; Canada; California.

130. Stibiconite, Sb0 4 , H 2 O.

Massive, powdery. H. =4 to 5’5; G. =5’28. Pale yellow. In closed tube yields water. C.c.: antimony 74’9, oxygen 19’6, water 5’5. Goldkronach (Bavaria).

131. Volgerite, SbO β , 5H 2 O.

Massive and powdery. White. In tube yields water, below redness. C.c.: antimony 58’9, oxygen 19’3, water 21’8. Constantine in Algeria.

132. Zundererz (Tinder Ore).

In soft, flexible, tinder-like masses. Colour dark cherry-red to blackish red; lustre glimmering. Two varieties :—one, from Klausthal, contains antimony oxide 33, iron oxide 40, lead 16, sulphur 4; the other, from Andreasberg and Klausthal, seems to be a mixture of jamesonite (82’04 per cent.), mispickel (13’46), and pyrargyrite (4’34).

133. Tellurite.

Yellowish or whitish. Radiated, spherical masses. Gives the reactions of tellurous acid. Facsebaya and Zalathna, Colorado.

134. Tantalic Ochre.

Powdery; brown; vitreous. Pennikoja in Finland.

2. Oxides of Carbon-Silicon Family (Binoxides).

135. Quartz, SiO 2 .

Hexagonal; the purest varieties tetartohedral. The primary pyramid P has the middle edge = 103° 34', and the polar edges -

133° 44', and is often perfect. Very frequently it appears as a rhombohedron R (or IP), with polar edges = 94° 15'. Crystals often of «P, P 6 or «P, P, 4P, the forms »P and 4P being combined in an oscillatory manner, producing striae on the face of the prism (figs. 303, 304, 305); also α>P, P, ⅛(2P2), the last face appearing as a rhomb replacing the alternate angles between the two other forms (figs. 307,308). They are prismatic, or pyramidal, or rhombohedral, when P is divided into R and -R; the latter very often wanting. Many faces plagihedral, as in figs. 302, 306, 309.

Twins common, with parallel axes, and either merely in juxtaposition (see fig. 178) or interpenetrating. Crystals often distorted, as in figs. 310 to 313. The crystals occur either single, attached, or imbedded, or in groups and druses. Most frequently granular, massive, fibrous, or columnar; also in pseudomorphs, petrifactions, and other forms. Cl. rhombohedral along R, very imperfect; prismatic along ooP, still more imperfect; fracture conchoidal, uneven, or splintery. H. = 7; G. =2’5 to 2’8; 2’65 in the purest varieties. Colourless, but more often white, grey, yellow, brown, red, blue, green, or even black. Lustre vitreous, inclining to resinous; transparent or translucent; when impure almost opaque. B. B.

infusible alone; with soda effervesces, and melts into a clear glass. Insoluble in acids, except the hydrofluoric; when pulverized, slightly soluble in solution of potash. C.c.:

48Ό5 silicon and 51’95 oxygen; but frequently a small amount of the oxides of iron or titanium, of lime, alumina, and other substances.

The following are varieties :—

Rock-crystal : highly transparent and colourless; Dauphiné, Switzerland, Tyrol, Hungary, Madagascar, and Ceylon.

Amethyst : violet-blue (from iron peroxide or manganese), and often marked by zigzag or undulating lines, and the colour disposed in clouds; Siberia, Persia, India, Ceylon, Brazil (white or yellow, named false topaz), Hungary, Ireland (near Cork), and Aberdeenshire. Wine-yellow (Citrin and Gold Topaz) ; the brown or Smoky Quartz (coloured by a substance containing carbon and nitrogen); and the .black or Morion, from Siberia, Bohemia, Pennsylvania, and other places. Cairngorm Stone, black, brown, or yellow, from Aberdeenshire mountains. The above are valued as ornamental stones; those which follow are less so.

Rose Quartz : red inclining to violet-blue; Clashnaree Hill (Aberdeen), and Rabenstein in Bavaria. Milk Quartz : milk-white, and slightly opalescent; Greenland. Prase: leek and other shades of green; Saxony and Cedar Mountain in South Africa. Cat's-eyr, inclosing asbestos: greenish white or grey, olive-green, red, brown, or yellow; Ceylon and Malabar. Avanturine, enclosing mica: yellow, red, green, or brown; India, Spain, and Scotland. Siderite: indigo or Berlin blue; Golling in Salzburg.

Common Quartz, crystallized or massive, white or grey, also red, brown, &c., is a frequent constituent in many rocks. Some impure varieties are properly rocks, as :—

(1) Ferruginous Quartz, or Iron Flint: red, yellow, or brown; often associated with iron ores.

(2) Jasper: red, yellow, brown, also green, grey, white, and black; alone, or in spots, veins, and bands (Ribbon or Egyptian Jasper)·, Urals,Tuscan Apennines, Harz, and many parts of Scotland.

(3) Lydian Stone, or Flinty Slate : black, grey, or white; has a splintery or conchoidal fracture, breaks into irregular fragments, and passes by many transitions into clay-slate, of which it is often merely an altered portion, as in Scotland; used as a touchstone for gold, and at Elfdal (Sweden) manufactured into ornaments.

(4) Hornstone or Chert : compact, conchoidal, splintery fracture; translucent on the edges; dirty grey, red, yellow, green, or brown; passes into flinty slate or common quartz; common in the Mountain limestone, Oolite, and Greensand formations; and often contains petrifactions, as shells, corals, and wood.

Other siliceous minerals seem intimate mixtures of quartz and opal, as:—

Flint : greyish white, grey, or greyish black, also yellow, red, or brown; sometimes in clouds, spots, or stripes; semitransparent; lustre dull; fracture flat conchoidal; occurs chiefly in the Chalk formation, as in England, Ireland, Aberdeenshire, France, Germany, and other countries; sometimes in beds or vertical veins, often in irregular lumps or concretions, inclosing petrifactions, as sponges, echinoids, shells, or siliceous Infusoria. The colour is partly derived from carbon, or organic matter. Used formerly for gun-flints, and still for the manufacture of glass and pottery; and cut into cameos or other ornaments.

Chalcedony : semitransparent or translucent; white, grey, blue, green, yellow, or brown; stalactitic, reniform, or botryoidal, and in pseudomorphs or petrifactions; Iceland, Faroes, Trevascus in Cornwall, Scotland, Hungary, Bohemia, Oberstem. Carnelian: chiefly blood-red, but also yellow, brown, or almost black; India, Arabia, Surinam, and Siberia; also Bohemia, Saxony, and Scotland (Fifeshire). Plasma: leek-or grass-green, and waxy lustre; Olympus, Black Forest, India, and China.

Chrysoprase: apple-green; Silesia, and Vermont in NorthAmerica. Moss-Agate and Heliotrope : dark green and dendritic (called Bloodstone when sprinkled with deep red spots); India, Siberia, Bohemia, Fassa Valley, island of Rum and other parts of Scotland.

136. Tridymite, SiO 2 .

Hexagonal; P middle edge 124° 4', polar edges 127° 35'. Single crystals, very minute hexagonal tables of 0P, α>P, but with the edges replaced by P and ∞P2, are rare (fig. 314). Mostly twinned in double or (offener) triple combinations (figs. 315 to 317). Cl. basal, indistinct; fracture conchoidal. H. = 7; G.-2’282 to 2’326. Colourless and transparent; vitreous, pearly on the base. B.B. like quartz. C.c.: 96 silica, with some alumina, magnesia, and iron peroxide, probably from the matrix. Discovered by Von Rath in the trachyte of San Cristobal, near Pachuca, in Mexico; also in the trachyte of Mont-Dore (Puy-de-Dôme), the Drachenfels, and Hungary. Many opals, treated with solution of potash, leave crystals, as those from Zimapan, Kaschau, Silesia, and the cacholong from Iceland. Where such crystals are abundant, the opal becomes opaque or snow-white. Jenzεch regards these as still another variety of silica.

137. Opal, 9SiO 2 , H 2 O to 3SiO 2 , H 2 O .

Amorphous; fracture conchoidal; very brittle. H. — 5 5 to 6’5; G. =2 to 2‘2. Transparent to opaque; vitreous, inclining to resinous. Colourless, but often white, yellow, red, brown, green, or grey, with a beautiful play of colours. B. B. decrepitates and becomes opaque, but is infusible; in the closed tube yields water; almost wholly soluble in solution of potash. C.c.: silica, with 5 to 13 per cent, water. Most opals are mixtures of various minerals.

The following varieties may be noticed:—(1) Hyalite, Glassy Opal, or Muller's Glass·, transparent, colourless, very glassy; small botryoidal, or incrusting; Kaiserstuhl in the Breisgau, Schemnitz, Silesia, Moravia, Mexico, and other places. (2) Fire Opal or Girasol∙. transpirent; brilliant vitreous lustre; bright hyacinth-red or yellow; Zimapan in Mexico, and the Faroes. (3) Noble Opal, semi-transparent or translucent; resinous, inclining to vitreous; bluish or yellowish white, with brilliant prismatic colours; most show double refraction and are binaxal; in irregular masses or veins near Eperies in Hungary; Australia. (4) Common Opal·. semitransparent, vitreous; white, yellow, green, red, or brown; Hungary, also Faroes, Iceland, the Giant’s Causeway, and the Western Isles of Scotland. (5) Semi-opal·, duller and less pellucid; Wood Opal or Lithoxylon∙. with the form and texture of wood distinctly seen; Hungary, Bohemia, and other countries. (6) Menilite∙. compact, reniform; opaque and brown or bluish grey; Menilmontant, near Paris. (7) Opal Jasper·. blood-red, brown, or yellow. (8) Cacholong∙. opaque, dull, glimmering, or pearly, and yellowish or rarely reddish white; in veins or reniform and incrusting; Faroes, Iceland, the Giant’s Causeway. One variety is named Hydrophane, from imbibing water, and becoming translucent. (9) Siliceous Sinter : deposited from the Geyser and other hot springs; and Pearl Sinter·, incrusting volcanic tufa at Santa Fiora in Tuscany (Fiorite), and in Auvergne.

138. Zircon, ZrO 2 , SiO 2 .

Pyramidal; P 84° 20'. Crystals, ∞P, P; often with 3P3; also αPα>, P; or a>P∞ (s), ∞P (Z), P (P), 3P3 (»), Poo (0, 4P4 (y), 5P5 (z), (fig. 318, also 86, 87, 585). Chiefly prismatic or pyramidal, and in rounded grains. Transparent to opaque; vitreous, often adamantine. Rarely white, generally grey, yellow, green, or frequently red and brown. B. B. loses its colour, but is infusible. Not affected by any acid except concentrated s. acid, after long digestion.

C. c.: 66 ’ 3 zirconia and 33 ’ 7 silica, with 0 to 2 iron peroxide as colouring matter. Miask, Arendal, Sweden, Belgium (at Nil-St-Vincent), Carinthia, Tyrol, Ceylon, and North America; in Scotland, Seal pay in Harris (fig. 319), Lewis (Hyacinth), Sutherland, Ross. The colourless varieties are sold for diamonds. The more brilliantly coloured are named hyacinths, and are valuable gems.

SULPHIDES, SELENIDES, TELLURIDES, &c.

139. Pyrite, FeS 2 .

Cubic; semitesseral dominant (figs. 320 to 323, also 67 to 77, and 26 to 34). Pentagonal-dodecahedron in excess; or striae, produced by oscillation of it with faces of the cube, visible. Often distorted, as in the cubo-octahedral twin (fig. 323). Sometimes massive and in pseudomorphs. Cl. cubic or octahedral, difficult; brittle. H. =6 to 6 ’ 5; G. = 4 - 9 to 5’2. Brass-yellow, often somewhat gold-yellow; streak brownish black, when broken emits smell of sulphur. In closed tube sulphur sublimes. B.B. on charcoal burns with blue flame, and odour of sulphurous acid. In inner flame fuses to magnetic bead. Sol. in n. acid, with deposition of sulphur. C.c.: iron 46‘7, sulphur 53'3; often contains gold in visible grains, when broken. Common to rocks of all ages. Tomnadashin, Birnam, Scotland; Cornwall, England; Elba and Traversella; Peru; Rossie, Middletown, and Schoharie in U.S. Auriferous pyrites, Berezoff (Siberia), Adelfors (Sweden), Mexico. Used to be cut in facets and set as an ornament, under the name of marcasites; also for striking fire in the old firelocks, whence the name of firestone; now used for manufacture of sulphuric acid.

140. Marcasite, FeS 2 .

Right prismatic; ooP (Jf) 106“ 5'. Crystals tabular, thin prismatic, or pyramidal. Twins very frequent, also cockscomb-like groups, or spherical and stalactitic. Cl. α>P; fracture uneven; brittle. G. =4’65 to 4 - 9. Greyish bronzeyellow to greenish grey, often with brown crust; streak greenish grey or brownish black. B.B., &c., like pyrite. Very prone to decomposition, being changed into green vitriol, which may be detected by the tongue.

Spear Pyrites are twins like fig. 325; Littmitz, Przibram. Hepatic Pyrites or Leberkies, liverbrown, generally decomposing; Harz, Saxony, Sweden. Cockscomb Pyrites; Derbyshire and the Harz. Kyrosite contains arsenic.

141. Mispickel, FeS 2 + FeAs.

Right prismatic; »P (3f) lll β 12' (fig. 326). Twins common; also massive or columnar. Cl. ooP; fracture uneven; brittle. H. = 5 , 5 to 6; G. =6 to 6’2. Silver-white to steel-grey; streak black. In closed tube yields first a red then a brown sublimate, lastly metallic arsenic. B.B. on charcoal fuses to a black magnetic globule. Sol. in n. acid, with separation of arsenious acid and sulphur. C.c.: 34’3 iron, 46 , 1 arsenic, 19 ’ 6 sulphur; sometimes silver or gold, or 5 to 9 of cobalt.

Cornwall, Freiberg, Zinnwald, Sweden, Franconia, America.

142. Leucopyrite, FeAs.

Right prismatic; α>P (rf) 122° 26'; Poo (o) 51° 20'. Crystals like fig. 327; generally massive or columnar. Cl. basal; fracture uneven; brittle. H. = 5 to 5 ’ 5; G. =7 to 7 4. Sil ver-white with darker tarnish; streak greyish black. B. B. emits strong smell of arsenic, and fuses to a black magnetic globule. C.c.: iron 27’2, arsenic 72 ’ 8; sometimes iron 32 ’ 2 and arsenic 66 - 8; always some sulphur, and often nickel and cobalt. Fossum in Norway, Andreasberg, Styria, and Silesia. Spathiopyrite, from Bieber in Hesse, seems a variety.

143. Cobaltite, CoS 2 + CoAs.

Cubic and hemihedral; sometimes massive (figs. 67, 74). Cl. cubic, perfect; brittle. H. =5 ’ 5; G. =6 to 6 ’ 3. Brilliant lustre. Pinkish silver-white; tarnishes yellow or grey; streak greyish black. B.B. with borax blue glass; evolves smell of arsenic. C.c.: cobalt 35 ’ 9, arsenic 44 ’ 9, sulphur 19 ’ 2. St Just in Cornwall, Tunaberg in Sweden, Skutteruα in Norway, Querbach in Silesia.

144. Glaucodote, (Co, Fe)S 2 + (Co, Fe)As a .

Right prismatic; ooP112°36'. Cl. basal, perfect. H. =5; G.= 6. Lustre metallic. Greyish white; streak black. C.c.: cobalt 24 ’ 7, iron 11 ’ 9, arsenic 43 ’ 2, sulphur 20 ’ 2. Huasco in Chili.

145. Smaltine, (Co, Fe, Ni)As 2 .

Cubic; generally like fig. 27; also reticulated and granular compact. Cl. octahedral; fracture uneven; brittle. H. =5’5; G. = 6 - 4 to 7 ’ 3. Tin-white to steel-grey, with dark or iridescent tarnish; streak greyish black. Evolves odour of arsenic, when broken or heated. C.c.: 71'4 arsenic, 28 ’ 6 cobalt; sometimes 3 to 19 iron, and 1 to 12 nickel, or 4 bismuth. Dolcoath and Redruth in Cornwall, Schneeberg, Annaberg, Tunaberg, Allemont, Chatham in Connecticut.

146. Chloantite ( White Nickel), NiAs.

Cubic; generally fine granular or compact; fracture uneven; brittle. H. = 5 - 5; G. =6’4 to 6 6. Tin-white, rapidly tarnishing black. In the closed tube yields a sublimate of arsenic, and becomes copper-red. Gives odour of arsenic when broken. B.B. fuses with much smoke, becomes coated with crystals of arsenious acid, and leaves a brittle grain of metal. C.c.: 28 - 2 nickel, 7Γ8 arsenic, but often with cobalt. Schneeberg, Riechelsdorf, Allemont, Chatham in Connecticut.

147. Gersdorffite, NiS 2 + NiAs 2 .

Cubic (figs. 74, 30, 26). Cl. cubic, generally granular. H. = 5 , 5; G. = 6 - 67. Lustre metallic. Silver-white to steel-grey, decrepitates in closed tube. B.B. fuses to a black slag; partially sol. in n. acid. C.c.: 35’2 nickel, 45’4 arsenic, and 19’4 sulphur; sometimes with cobalt. Craignuir, near Loch Fyne, with 23 nickel and 6 cobalt. The Harz, Sweden, Spain, and Brazil.

148. Ullmannite, NiSb + NiS 2 .

Cubic (figs. 31, 29, 27); often tetrahedral, and in twins as in figs. 328, 329. Cl. cubic, perfect; fracture uneven. H. = 5 to 5 ’ 5; G. =6 2 to 6’5. Lead-grey to tin-white, often with iridescent tarnish. B.B. fuses with dense fumes. Sol. in n. acid. C.c.: 27’4 nickel, 57'5 antimony, and 15’1 sulphur. Westerwald, Siegen, Harzgerode, Lölling (Carinthia), Lobenstein, and Bleiberg.

149. Rammelsbergite, NiAs.

Right prismatic; ooP 123° to 124°. Chiefly massive, or in radiating and botryoidal aggregates. H. =5; G. =7’2. Colour tin-white. Schneeberg, Reichelsdorf, and Wittichen in Baden.

150. Hauerite, MnS 2 .

Cubic (figs. 30, 30-26, 30-33-37). Crystals single or in spherical groups. Cl. cubic, perfect; H. =4; G. = 3’46. Reddish brown to brownish black; streak brownish red. In closed tube yields sulphur, and leaves a green mass, which is sol. in h. acid. C.c.: 46 manganese and 54 sulphur. Kalinka in Hutιgary.

151. Pyrrhotite {Magnetic Pyrites), Fe 7 S 8 .

Hexagonal; P126° 48'. Crystals rare, sometimes hemihedral on z⅛, commonly massive or granular. Cl. ∞P, imperfect; brittle. H. = 3 - 5 to 4 - 5; G. = 4 '5 to 4 ’ 6. Colour bronze-yellow with pinchbeckbrown tarnish; streak greyish black. More or less magnetic. C. c.:

63 - 65 iron and 36’35 sulphur; sometimes with nickel. Common in primary limestones and diorites of Scotland. Crystallized in above forms at Askaig, on Loch Shin, Sutherland; Carnarvon, Cornwall, Fahlun, Bodenmais, Andreasberg. Distinguished by its colour and its solubility in h. acid.

152. Linnaeite, 2(Co, Cu)S + CoS 2 .

Cubic (figs. 29, 30); often twinned; twin face O; also massive. Cl. cubic; brittle. H. =5’5; G. =4’9 to 5. Sil ver-white, with a yellow tarnish; streak blackish grey. B. B. fuses to a grey magnetic globule, which is bronze-yellow when broken. C.c.: cobalt 43’2, copper 14’4, iron 3’5, sulphur 38’5. Bastnaes (Sweden).

153. Siegenite, CoS + Ni 2 S 8 (f).

Cubic; generally in crystals like fig. 29; also massive. Colour silver-white, inclining to pink. Other features likelinnaeite. C.c.: cobalt 40’8, nickel 14’6, sulphur 43Ί. Müsen near Siegen, Maryland, and Missouri. The American mineral has 30’5 of nickel.

154. Polydymite, Ni 4 S 5 .

Cubic; in minute octahedral crystals and flattened twins. Cl. cubic. H. —4'5; G. = 4 - 81. C.c.: 39’45 nickel, 40’55 sulphur, but generally with 4 of iron. Westphalia. Saynite or grunauite seems to be a bismuthic and cobaltic variety; it is from Grunau in Sayn-Altenkirchen.

155. Byrichrite, 3NiS + 2NiS a .

H.=3 to 3’5; G.-4 ’ 7. C.c.: 54’23 nickel, 2’79 iron. 42’86 sulphur. From the Westerwald.

156. Horbachite, 4Fe 2 S 8 + Ni 2 S 3 .

Crystalline masses. H.-4’5; G. =4’43 to 4’7. Colour pinchbeck-brown; streak black. C.c.: nickel 11 ’98, iron 41 ’96, sulphur 45’87. Horbach in the Black Forest.

157. Skutterudite, CoAs 8 .

Cubic (figs. 30, 26 with 33, 40) and granular. Cl. cubic; fracture conchoidal; brittle. H. =6; G. = 6’74 to 6’84. Tin-white to lead-grey. Lustre brilliant. In closed tube gives sublimate of metallic arsenic, otherwise like smaltine. C.c.: 79 arsenic, 21 cobalt. Skutterud, near Modum in Norway.

158. Galena, PbS.

Cubic; crystals chiefly cube, octahedron, and rhombic dodecahedron; rarely 20 and 202. Also massive and granular, compact, or laminar, and in pseudomorphs of pyromorphite and other minerals. Cl. cubic, very perfect; fracture scarcely observable; sectile.

H. = 2’5; G.=7∙2 to 7’6. Lead-grey, with darker or rarely iridescent tarnish; streak greyish black. B.B. decrepitates, fuses, and leaves a globule of lead. Sol. in n. acid. C.c.: 86’7 lead, and 13’3 sulphur; but usually contains a little silver, ranging from 1 to 3 or 5 parts in 10,000; rarely 1 per cent, or more. Some contain copper, zinc, or antimony, others selenium, and others (the “supersulphuret ”) probably free sulphur (2 to 8 per cent.). Most common ore of lead in many countries. Leadhills, Pentland Hills, Linlithgow, Inverkeithing, Monaltrie, Tyndrum, Strontian, Islay, Orkney, Cornwall, Derbyshire (Castletown), Cumberland (Alston Moor), Durham (Allenhead), Wales, Isle of Man.

159. Cuproplumbite, 2PbS + Cu 2 S.

Cubic. H. =2’5; G. =»6’4. Bluish grey. Chili.

160. Beegerite, 6PbS + Bi 2 S 3 .

Cubic. G. = 7∙27. Cl. cubic. Light to dark grey. Lustre brilliant. C.c.: sulphur 15, bismuth 20’6, lead 64’2, with copper 1’7. Grant (Park county, Colorado).

161. Clausthalite, PbSe.

Cubic; but massive granular. H. = 2 - 5 to 3; G. = 8 ’ 2 to 8’8. Lead-grey; streak grey. B. B. fuses, smells of selenium, colours the flame blue, stains the support red, yellow, and white, and volatilizes, except a small residue, without fusing. C.c.: 72’7 lead, 27'3 selenium; but sometimes 11’7 of silver. Zorge, Lerbach, and Clausthal in the Harz. Tilkerodite, or Selen-Cobalt-Blei, containing 3 per cent, of cobalt, from Tilkerode, is a variety.

162. Zorgite.

Massive granular; like clausthalite, but inclining to reddish, and often tarnished. There are four varieties, (a) Sden-Blei-Kupfer: G. =7’4 to 7’5; 5PbSe + CuSe; with 4 copper, 65lead, 30 selenium. (5) The same, but with G. — 5’6; 4Pb, 4Cu, 7Se; with 15’8 copper, 48’4 lead, and 35 selenium, (c) Selen-Kupfer-Blei: with G. =7; 2PbSe + CuSe; with 8 copper, 57 lead, and 32 selenium, {d) 2PbSe + 9CuSe; with 46’64 copper, 16’58 lead, and 36’59 selenium. From Tilkerode and Zorge in the Harz, and near Gabel in Thuringia.

163. Altaite, PbTe.

Cubic and granular; fracture uneven; sectile. H. =3 to 3’5; G. — 8 Ί to 8 , 2. Tin-white to yellow, with yellow tarnish. B. B. colours the flame blue, fusing to a globule, which almost wholly volatilizes. C.c.: 61’9 lead and 38Ί tellurium. Zavodinski in the Altai, California, Colorado, and Chili.

164. Redruthite {Copper Glance), Cu 2 S.

Right prismatic. ooP (o) 119° 35'; P {P) middle edge 125 β 22'; I? {a) middle edge 65° 40'; 2^oo {d) middle edge 125°40'; ∣f∞ {e) middle edge 65° 48'. Crystals 0P {s), ∞P {o), oofoo {p) (figs. 333,

334); with hexagonal aspect; also twins; and massive. Cl. ∞P, imperfect; fracture conchoidal or uneven; sectile. I⅜ = 2 ’ 5 to 3; G. = 5'5 to 5 ’ 8. Rather dull; brighter on the streak. Blackish lead-grey, with a blue or other tarnish. B.B. colours the flame blue; on charcoal in the oxygen flame sputters, and fuses easily; in the red. flame becomes solid. With soda gives a grain of copper. Green solution in n. acid, leaving sulphur. C.c.: 79’8 copper, 20'2 sulphur. Fassnet Burn (Haddingtonshire), Ayrshire, Fair Island, near Redruth and Land’s End in Cornwall, Saxony, Silesia, Norway, the Banat, Siberia, and the United States. Important copper ore.

165. Stromeyerite, Cu 2 S + AgS.

Right prismatic; isomorphous with redruthite. Crystals rare; usually massive; fracture flat, very sectile. H. =2'5; G. =6'2 to 6'3. Bright. Blackish lead-grey. C.c.: 53Ί silver, 3Γ2 copper, and 15 '7 sulphur, but often indeterminate proportions of silver (3 to 53) and copper (30 to 75). Schlangenberg in Siberia, Rudelstadt in Silesia, and Catemo in Chili.

166. Berzelinite, Cu a Se.

Crystalline, in thin dendritic crusts, and imbedded in calcite. Silver-white with a black tarnish; streak shining. In open tube gives a red sublimate of selenium, with white crystals of selenious acid. B.B. on charcoal fuses to a grey, slightly malleable bead, giving odour of selenious acid; with soda a grain of copper. C.c.: 61'5 copper and 38 '5 selenium. Skrikerum in Smäland, Lerbach in the Harz.

167. Crookesite, (CuTl) 3 Se.

In crystalline grains the size of peas. H. —2'5 to 3; G. = 6 9. Brittle. Lead-grey. Metallic. B.B. colours the flame intense green. C.c.: 45'76 copper, 3'71 silver, 17'25 thallium, 33'27 selenium. From Skrikerum.

168. Eukairite, Cu 2 Se + AgSe.

Massive and granular crystalline. Cuts with knife. Lead-grey; streak shining. B.B. fuses to a brittle metallic grain. C.c.: 431 silver, 25 '3 copper, and 31 '6 selenium. Skrikerum, Atacama, Chili.

169. Argentite, Ag 2 S .

Cubic. ∞O∞; Ο; 00O; and 202 (figs. 29, 56). Crystals generally misshapen, with uneven or curved faces; in druses, or linear groups; also arborescent, capillary, or in crusts. Cl. indistinct; fracture hackly; malleable and flexible. H. =2 to 2'5; G. =7 to 7 '4. Rarely brilliant, more so on the streak. Blackish lead-grey, often with a black, brown, or rarely iridescent tarnish. B.B. on charcoal fuses, intumesces greatly, and leaves a grain of silver. Sol. in con. n. acid. C.e.: 87 silver and 13 sulphur. Huel Duchy, Dolcoath, Herland, and near Callington in Cornwall; Alva in Stirlingshire: Freiberg, Marienberg, Annaberg, Schneeberg, Johann-Georgenstadt, Joachimsthal, Schemnitz and Kremnitz, Kongsberg. Common ore at Guanajuato and Zacatecas in Mexico, in Peru, and at Blagodat in Siberia.

170. Acanthite, AgS.

Right prismatic. H. =2'5; G. = 7'33. Iron-black. C.c. like argentite, thus dimorphous. Freiberg and Clausthal, on argentite; also at Copiapo.

171. Jalpaite, 3AgS + Cu 2 S.

Cubic; form 0. Cl. cubic; malleable. H. =2'5; G. = 6'88. Darkgrey. Metallic lustre. C.c.: silver 71'78, copper 14 04, sulphur 14'2. Jalpa in Mexico.

172. Lautite (CuAg) As.S.

Granular. Iron-black. H. =3; G. =4'96. C.c.: copper 28'3, silver 12, arsenic 41'8, sulphur 17'86. Lauta, near Marienberg.

173. Naumannite, AgSe.

In thin plates and granular. Cl. hexahedral, perfect. Malleable. H. =2'5; G. =8. Iron-black. Splendent. C.c.: 73 silver and 27 selenium, with 4'91 lead. Tilkerode.

174. Hessite, AgTe.

Cubic or anorthic (?); massive and granular. Slightly malleable. H. = 2'5 to 3; G. = 81 to 8'45. Blackish lead-grey to steelgrey. B. B. on charcoal fumes, fuses to a black grain with white spots, and leaves a brittle grain of silver. C.c.: 62'8 silver and 37'2 tellurium. Zavodinski (Altai), Nagyag, Rezbanya, California, and Chili.

175. Petzite, 2AgTe + AuTe.

Like hessite. Two varieties :— (a) with G. =8'72, containing 18 per cent, of gold, from Nagyag; (δ) with G. =9 to 9'4, and 24 to 26 of gold. Calaveras and Tuolumne in California, Colorado.

176. Discrasite, Ag 2 Sb; Ag 3 Sb; and Ag β Sb.

Right prismatic; P with polar edges 132° 42' and 92°; ∞P 120° nearly (figs. 335, 336). Crystals short prismatic, or thick tabular, and vertically striated (fig. 335); twins united by a face of ∞P; often in stellar groups (fig. 336); also massive or granular. Cl. basal and P∞, distinct; 00P imperfect; rather brittle, and slightly malleable. H. =3'5;

G. = 9 '4 to 9 '8. Silver-white to tin-white, with a yellow or blackish tarnish. B. B. fuses easily, fumes staining the charcoal white, and leaves a grain of silver. Sol. in n. acid. C.c.: 64 to 84 silver, and 36 to 16 antimony. Andreasberg, Allemont in Dauphiné, Spain, and Arqueras in Coquimbo (Chili). A valuable ore of silver. A variety from Chili contains 94'2 silver and 5'8 antimony, and is Ag lβ Sb.

177. Blende, ZnS.

Cubic and tetrahedral (figs. 152, 153, 337). Twins remarkably common, united by a face of 0, and several times repeated; frequently massive and granular. Cl. ∞O, perfect; very brittle. H. = 3'5 to 4; G. =3'9 to 4'2. Semitransparent to opaque; adamantine and resinous. Brown or black, also red, yellow, and green, rarely colourless or white. B.B. decrepitates, often violently, but only fuses on very thin edges. Sol. in con. n. acid, leaving sulphur. C.c.: 67 zinc and 33 sulphur; but generally in the darker varieties with 1 to 15 iron, 0 to 3 cadmium.

Very abundant. Glen Gairn (bright yellow and highly phosphorescent), Leadhills. Tyndrum, Cornwall, Derbyshire, Cumberland, the Harz, Freiberg, Przibram, Schemnitz, Kapnik, North America, Peru. Used for producing zinc vitriol and sulphur, and as an ore of zinc. Lithium, indium, thallium, and gallium have all been found in blende.

178. Wurtzite, 6ZnS + FeS.

Hexagonal; 00P, P, with well-marked horizontal striae. Cl. basal, and prismatic. H. = 3'5 to 4; G. =3'9 to 4Ί. Brownish black; streak light brown. C.c.: like blende, which is thus dimorphous. Oruro in Bolivia, and Przibram (radiated and cadmiferous).

179. Greenockite, CdS.

Hexagonal, and generally hemimorphic. P 86° 21'; 2P 123° 54 , . Crystals 2P, OP, 00P, P; orP, 2P, 00P; attached singly. Cl. 00P, imperfect; basal perfect. H. =3 to 3'5; G. =4'8 to 4'9. Translucent; brilliant resinous, or adamantine. Honey-or orange-yellow, rarely brown; streak yellow. B. B. decrepitates, and becomes carmine-red, but again yellow when cold; fused with soda forms a reddish brown coating on charcoal. Sol. in h. acid. C.c.: 77'6 cadmium, and 22'4 sulphur. Bishopton in Renfrewshire, Przibram, and Friedensville in Pennsylvania.

180. Alabandine, MnS.

Cubic; 0 and ooθ∞; usually massive and granular. Cl. hexahedral, perfect; fracture uneven; rather brittle. H. =3'5 to 4; G. = 3 '9 to 4. Opaque; semi-metallic. Iron-black to dark steelgrey, brownish black tarnish; streak dark green. B.B. fuses on thin edges to a brown slag. Sol. in h. acid. C.c.: 63 manganese and 37 sulphur. Nagyag, Kapnik, Alabanda in Caria, Mexico, and Brazil.

181. Millerite, NiS.

Hexagonal rhombohedral; R 144° 8'; in fine acicular prisms of ∞P2, R. Brittle. H. =3'5; G. =4'6 (or 5 26 to 5'65). Brass-or bronze-yellow, with a grey or iridescent tarnish. B.B. fuses easily to a blackish metallic globule, which boils and sputters. In nitro-hydrochloric acid forms a green solution. C.c.: 64 '4 nickel and 35'6 sulphur. Morven (Argyllshire), Chapel (Fife), Ayrshire, near St Austell in Cornwall, at Merthyr-Tydvil, Johann-Georgenstadt, Joachimsthal, Przibram, Camsdorf, Riechelsdorf, Pennsylvania.

182. Pentlandite (Eisennickelkies), 2FeS + NiS.

Cubic; massive and granular; fracture uneven; brittle. H. — 3'5 to 4; G. =4'6. Light pinchbeck-brown, with darker streak. Not magnetic. B.B. acts in general like pyrrhotite; the roasted powder forms with borax in the réd. flame a black opaque glass. C.c.: 36 sulphur, 42 iron, and 22 nickel; but mixed with pyrrhotite and chalcopyrite. Lillehammer in southern Norway. Inverarite, 5FeS + NiS, with 11 of nickel, from near Inveraray, is a variety.

183. Nickelite (Copper Nickel), NiAs.

Hexagonal; P 86° 50 ’. Crystals 00P, OP; rare. Arborescent, reniform, and massive; fracture conchoidal and uneven; brittle. H. = 5 '5; G. = 7 '5 to 7 '7. Light copper-red, with a blackish tarnish. It forms no sublimate in the closed tube. B. B. fuses with strong fumes to a white, brittle, metallic globule. C.c.: 43 - 6 nickel and 56'4 arsenic. Hilderston in Linlithgow, Pibble in Kirkcudbright, Leadhills, Pengelly and Huel Chance in Cornwall, Freiberg, Schneeberg, Joachimsthal, Sangerhausen, Andreasberg, Chatham in Connecticut. Used as an ore of nickel.

184. Breithauptite (Antimonial Nickel), NiSb.

Hexagonal; P 86° 56'. Crystals, thin striated hexagonal tables of OP, ∞P. H.-5; G. — 7'5to7'6. Brilliant. Light copper-red, generally with violet tarnish. B.B. fumes, but fuses with great difficulty. C.c.: 32‘2 nickel and 67’8 antimony. Andreasberg.

185. Stannite (Tin Pyrites), 2CuS, SnS 2 + 2(FeS, ZnS) + SnS 2 .

Cubic; in cubes very rare, generally massive and granular. Cl. hexahedral, imperfect; fracture uneven or small conchoidal; brittle. H. =4; G. =4’3 to 4 - 5. Steel-grey; streak black. C.c.: 26 to 32 tin, 24 to 30 copper, 5 to 12 iron, 2 to 10 zinc, and 30 sulphur. Huel Rock near St Agnes, St Michael’s Mount, and Carn-brea in Cornwall; Zinnwald. Bell-metal ore.

186. Sternbergite, (AgS + 2FeS)FeS 3 .

Right prismatic; P middle edge 118°. Crystals usually thin tabular; in twins, or in fan-like and spheroidal groups. Cl. basal, perfect; sectile, and flexible in thin laminae. H. = 1 to 1'5; G. = 4 - 2 to 4 , 25. Dark pinchbeck-brown, often a violet-blue tarnish; streak black. C.c.: 34 ’ 2 silver, 35 - 4 iron, and 30 - 4 sulphur. Joachimsthal, Schneeberg, and Johann-Georgenstadt. Flexible Sulphurct of Silver, from Hungary and Freiberg, is identical. Frieseite, Ag 2 Fe 5 S 8 , in twins (fig. 339), is a variety.

187. Rittιngerite, AgAs.

Oblique prismatic. ∞P 126 β 18'; ooPoo and OP. Cl. basal; fracture conchoidal; brittle. H. =2‘5to3; G. =5 ’ 63. C.c.: silver 577, the remainder being arsenic, with someselenium. Joachimsthal, Silesia, Felsöbanya in Hungary.

188. Covelline, CuS.

Hexagonal. Crystals α>P, OP; rare; usually reniform and granular. Cl. basal; sectile. Thin laminae flexible. H. =15 to 2; G. — 3'8 to 46. Resinous. Indigo-blue; streak black. B.B. burns with blue flame. Sol. in n. acid. C.c.: 667 copper, 33 - 3 sulphur. Cairnbeg in Cornwall, Vesuvius, Leogang (Austria), Chili, Angola, New Zealand, and Victoria.

189. Chalcopyrite (Copper Pyrites), CuS + FeS.

Pyramidal; and sphenoidal hemihedric; ⅜P (P) with polar edges 71° 20'; ooP∞. Crystals generally small and deformed; twins very common, like fig. 340. P∞(δ) 89° 10', 2P<≈o(c) 126° 11',

0P (a), P (fig. 89). Most commonly compact and disseminated; also botryoidal and reniform. Cl. pyramidal 2P∞; sometimes rather distinct; fracture conchoidal or uneven. H. =3 ’ 5 to 4; G. = 41 to 4 ’ 3. Brass-yellow, often with a gold-yellow or iridescent tarnish (peacock copper ore); streak greenish black. B.B. on charcoal becomes darker or black, and on cooling red; fuses easily to a steel-grey globule, which at length becomes magnetic, brittle, and greyish red on the fractured surface; with borax and soda yields a grain of copper; moistened with h. acid, colours the flame blue. C.c. essentially 1 atom copper, 1 atom iron, and 2 atoms sulphur; with 34’5 copper, 30'5 iron, and 35 sulphur. The most abundant ore of copper. In Kirkcudbrightshire and Wigtownshire, Tyndrum in Perthshire, Inverness-shire, Lairg in Sutherland, Shetland, Anglesea (Parys mine), Derbyshire, Staffordshire, Cumberland, Gunnislake (Devonshire), St Austell (Cornwall), Wicklow, Falun, Röraas, Freiberg, Mansfeld, Goslar, Lauterberg, Müsen, Siberia. It is distinguished from pyrite by yielding readily to the knife, by its tarnish, and by forming a green solution in n. acid.

190. Bornite (Purple Copper), 3Cu a S, Fe 2 S 3 .

Cubic. Crystals α>Ooo,and ooOoo, O; but rare, and generally rough or uneven; also twins. Mostly massive. Cl. octahedral; fracture conchoidal; slightly brittle; sectile. H. = 3; G. = 4 - 9 to 5'1. Colour between copper-red and pinchbeck-brown, with tarnish at first red or brown, then violet or sky-blue; streak greyish black. B. B. acts like chalcopyrite. Soluble in con. h. acid, leaving sulphur. C.c.: 55 - 6 copper, 16 '4 iron, and 28 sulphur. Crystals near Redruth and St Day in Cornwall; massive at Killarney in Ireland; also Norway, Sweden, Mansfeld, Silesia, Tuscany, and Chili. An ore of copper.

191. Cuban, CuS, Fe 2 S 3 .

Cubic. H. = 4; G. — 4 ’ 1. Bronze-yellow; streak bronze-yellow and black. Barracanao in Cuba, Tunaberg and Kafveltorp in Sweden.

192. Domeykite, Cu β As.

Botryoidal or massive; fracture uneven; brittle. H. =3 to 3*5; G. — 7 to 7 ’5. Tin-or silver-white, inclining to yellow, with an iridescent tarnish. Not affected by h. acid. C.c.: 7Γ63 copper and 28*37 arsenic. Calabazo in Coquimbo, and Copiapo in Chili. Con-durrite, massive, seems an impure variety; from Condurrow mine and near Redruth (Cornwall). Algodonite from Lake Superior, IP hit-neyite from Mexico, and Darwinite (88 copper) are also identical or similar.

193. Melonite, Ni 2 Te 3 .

Hexagonal; minute tabular crystals, foliated and granular. Metallic lustre. Reddish white; streak dark grey. C.c.: nickel 21, silver 4*1, tellurium 73*4. Stanislaus and Calaveras (California).

194. Sylvanite, AgTe 4 + AuTe 3 .

Oblique prismatic, C 55° 21'. ∞P 94° 26'; - P 0 oo 19° 21'; P c ∞ 62° 43'. Crystals small, short acicular, and often twinned and grouped in rows like letters; sectile, but friable. H. = 1 - 5 to 2; G. — 7 , 99 to

8’33. Steel-grey to silver-white, and pale bronze-yellow. C.c.: 59*6 tellurium, with 0 - 6 to 8*5 antimony, 26*5 gold (in some 30), and 13*9 silver, with 0*2 to 15 lead. Offenbanya (Graphic Tellurium), Nagyag (Yellow Tellurium), and California.

195. Nagyagite, Black Tellurium.

Pyramidal. P 137° 52'; P∞ 122° 50'; and 0P (fig. 343). Crystals tabular, rare; in general in thin plates or foliated. Cl. basal, perfect; sectile; thin laminae flexible. H. = 1 to 1*5; G. = 6 *85 to 7 *2.

Splendent. Blackish lead-grey. C.c.: 51 to 63 lead, 6 to 9 gold, 1 copper and silver, 13 to 32 tellurium, 3 to 12 sulphur, and 0 to 4*5 antimony. Nagyag and Offenbanya in Transylvania.

196. Maldonite, Au 2 Bi.

H.=l*5 to 2; G. =8 2 to 97. Colour silver-white, with black tarnish. C.c.: gold 64*5, bismuth 35*5. Occurs in granite veins at Maldon in Victoria.

197. Chilenite, Ag 10 Bi.

Minute plates of metallic lustre. Silver-white, but tarnished red or yellow. Silver 83 9, bismuth 16*1. From the mine San Antonio near Copiapo in Chili.

198. Cinnabar, HgS.

Hexagonal and rhombohedral; R 71° 48'. R (n),0R (o), ∞ R(m). ⅜R (i) (fig. 344). Crystals rhombohedral; also granular, compact, and earthy. Cl. ooR, perfect; fracture uneven and splintery; sectile. H. =2 to 2*5; G. =8 to 8’2. Transparent, with circular polarization. Adamantine. Cochineal-red; streak scarlet. C. c.: 86 *2 mercury, 13 *8 sulphur. Idria in Carniola, Almaden iu Spain, Wolfstein in Bavaria, Saxony, Hungary, Tuscany, China, California, Mexico, Peru. Chief ore of mercury. Also a pigment. Hepatic Cinnabar is a bituminous mixture.

199. Tiemannite, HgSe.

Fine granular; brittle. H.— 2*5; G.—71 to 7*4. Brilliant. Dark lead-grey. C.c.: 75 mercury, 25 selenium. Clausthal and Zorge.

200. Lerbach ite, (PbHg)Se .

Granular and massive. G. — 7*8 to 7*88. Colour steel-grey to iron-black. Brittle. Lerbach, Tilkerode in the Harz.

201. Guanajuatite, Bi 2 Se 3 .

Massive; granular; foliated and fibrous. II. = 2 *5 to 3; G. = 6*25. Blue-grey; streak grey and shining. Metallic; soft and malleable. C.c.: selenium 34*3, sulphur 7, bismuth 65. Santa Rosa (Guanajuato, Mexico).

202. Coloradoite, HgTe .

Massive and granular. H. =3; G. =8’63. Metallic. Iron-black. Conchoidal fracture. C.c.: 61 mercury, 39 tellurium. Colorado.

203. Molybdenite, MoS .

Hexagonal (?). Crystals OP, ocP; and OP, ∞P,P. Generally scaly. Cl. basal, perfect; sectile and flexible. Feels greasy. H. =1 to 1’5; (». = 4’6 to 4’9. Lead-grey with red tinge; grey streak on paper, greenish on porcelain. B.B. colours flame siskin-green; on charcoal yields sulphurous fumes, and forms a white coating; in warm nitrochloric acid a greenish, and in boiling s. acid a blue solution. C.c.: 59 molybdenum, 41 sulphur. In granular limestones, and in granites in Sutherland, Ross, Aberdeen, Argyll, and Kirkcudbright; Shap in Westmoreland, Caldbeckfell in Cumberland, Arendal, Zinnwald, Mont Blanc, Maine, Connecticut, Yea in Victoria. Used for preparing blue carmine, for colouring porcelain.

204. Laurite, (RuOs) 2 S 8 .

Cubic. Crystals 0, ∞O∞; oo03, ooOoo. Cl. octahedral. H. = 7 ’5; G. = 6 '99. Metallic, bright. Dark iron-black. Powder grey. Brittle. C.c.: ruthenium 65’18, osmium 3’03, sulphur 31’79. From platinum grains, in Borneo and Oregon.

205. Realgar, AsS.

Oblique prismatic. ooP (Λf) 74° 26'; P® ∞ (n) 132° 2', ∞P 0 2 (I) 113° 16'. Crystals (fig. 346) generally prismatic; sometimes massive. Cl. basal, also clino-X∖

diagonal; fracture splintery; sectile. K∖

H.=l’5to2; G.=3∙4 to 3’6. Trans-A z p :;: ∕Γ∕ parent to opaque; resinous. Aurora-red;: ∖ ·

streak orange-yellow. C.c.: arsenic 70,; ∣ ~ι- ∣—if:: ·

sulphur 30. Nagyag, Felsöbanya, St: j r

Gotthard, Vesuvius. > ∕ fl J. j

206. Orpiment, As 2 S 3 . ,1...,.- ·· ' ∖

Right prismatic. ooP 117° 49'. Fre-f ∕ ∕ f quently foliated. Cl. brachydiagonal; X. ‘ ∙∕∖ striated vertically; sectile and flexible.

H. =1’5 to 2; G. =3’4 to 3’5. Semi- < uβ , 9n ,> transparent; resinous to pearly. Citron- δ- ' p, yellow and orange-yellow. C.c.: arsenic 61, sulphur 39. Servia, Kapnik, Andreasberg, Solfatara, Zimapan in Mexico.

207. Dimorphite, As 2 S 3 .

Right prismatic. H. = 1’5; G. =3’58. Orange-yellow. Solfatara.

208. Stibnite, Sb 2 S 3 .

Right prismatic. P polar edges 109° 26' and 108° 21'; ooP 90° 54'. Crystals (fig. 347) generally prismatic. Cl. brachydiagonal, perfect; sectile. H. = 2;

G. =4’6 to 4’7. Brilliant lead-grey, often tarnished. C.c.: antimony71’8, sulphur 28 ’2. Maisley, Banffshire; Harehill, Ayrshire; Glendinning, Dumfriesshire; Endellion and Padstow, Cornwall; Wolfsberg, Harz; Przibram, Schemnitz, Auvergne, Spain, America, Melbourne. Chief ore of antimony.

209. Bismuthine, Bi 2 S 3 .

Kight prismatic. ooP 91° 30'. Crystals prismatic, striated; also granular and foliated. Cl. brachydiagonal; sectile. H. =2 to 2’5; G. =6’4 to 6’6. Lead-grey. C.c.: 81’2 bismuth, 18’8 sulphur. Caldbeckfell (Cumberland), Redruth (Cornwall), Riddarhyttan and Bastnaes (Sweden), Altenberg, Haddam (Connecticut), Ballarat (Victoria), Bolivia.

210. Frenzelite, Bi 2 Se 3 , or 2Bi 2 Se 8 +Bi 2 S 3 .

Right prismatic; ooP 90°. Needle crystals, and massive. Cl. brachydiagonal. H. =2’5 to 3; G. =6’25. Bluish grey; streak greyish black, shining. Lustre metallic. Malleable. C.c.: bismuth 67’38, selenium 24Ί3, sulphur 6’6. Guanajuato (Mexico).

SULPHUR SALTS.

211. Guejarite, Cu 2 S + 2Sb 2 S 8 .

Right prismatic. ooP 101° 9'. Cl. brachydiagonal. H. — 3’5; G. = 5’03. Steel-green, with bluish streak. C.c.: copper 15’5, antimony 58 , 5, sulphur 25. Guejar in Sierra Nevada.

212. Miargyrite, AgS + SbS 3 .

Oblique prismatic, C 81° 36'. P 90° 53';-P 59° 59'. Crystals pyramidal, or tabular (fig. 348); massive; sectile. H. =2 to 2’5; G. = 5 ’2 to 5’3. Metallic adamantine. Blackish lead-grey to steel grey; streak cherry-red. C.c.: 37 silver, 41 antimony, 22 sulphur. Freiberg, Przibram, Potosi.

213. Morocochite {Silber-Wismuth Glanz), AgS + BiS 3 .

Massive. Colour grey; streak light green. G. =6’92. C.c.: silveι 28’3, bismuth 54’7, sulphur 17. Morococha in Peru.

214. Sartorite, PbS + As 2 S 3 .

Right prismatic. Crystals slender; ooP 123° 20'. Cl. 0P. H. — 3 G. =5’39. C.c.: lead 42’68, arsenic 30’93, sulphur 26’39. Binnen thaï in Switzerland.

215. Zinckenite, PbS + SbS 3 .

Right prismatic. ooP {d) 120° 39'; fαo (o) 150° 36' (fig. 349). Crystals acicular; vertically striated, and twinned 3 or 6. Sectile. H.=3 to 3’5; G. = 5’3 to 5’35. Steel-grey to lead-grey; with blue tarnish. C.c.: lead 35’9, antimony 42, sulphur 22Ί. Wolfsberg.

216. Emplectite, CuS + Bi 2 S 8 .

Right prismatic. Tin-white. Saxony, Wiirtemberg, and Copiapo.

217. Wolfsbbrgite, Cu 2 S + Sb 2 S 3 .

Right prismatic. ∞P 135° 12'; ∞P2 111°. Crystals tabular: also fine granular. Cl. brachydiagonal, perfect; fracture conchoidal oruneven. H. =3’5; G. =4’748. Lead-grey to iron-black,sometimes iridescent; streak black, dull. C.c.: 25’4 copper, 49 antimony, and 25’6 sulphur. Wolfsberg.

218. Berthierite, FeS, SbS 3 .

Massive; columnar or fibrous, with indistinct cleavage. H. — 2’3; G. =4 to 4’3. Dark steel-grey, reddish. Tintagel and Padstow in Cornwall, Auvergne and Anglars (Creuse) in France, Braunsdorf in Saxony. In France used as an ore of antimony.

219. Plagionite, Pb 4 Sb 8 .

Oblique prismatic, C 72° 28'. P 134° 30' and 142° 3'; -2T 120° 49'. Crystals thick, tabular (fig. 350), minute, and in druses. Cl.-2P,perfect;brittle. H.=2’5; G.=5∙4. Blackish lead-grey. C.c.: 41 lead, 38 antimony, and 21 sulphur.

Wolfsberg.

220. Klaprothite, 3Cu 2 S + 2Bi 2 S 8 .

Right prismatic; long striated crystals; ∞P = 107°. Wittichen, Bulach. Schirmerite, from Colorado, 3(Ag 2 Pb)S + 2Bi 2 S 3 , with G. = 6’74, is similar.

221. Binnite, 3CuS + 2As 2 S 8 .

Cubic. Typical forms ooO, 202; O, ooθ∞, 606; 404, 10O10 3O∣. H. =4’5; G. = 4’48. Metallic. Black. Binnen.

222. Jamesonite, 3PbS + 2Sb 2 S 3 .

Right prismatic; ooP 101° 20'. Crystals ooP, οοϊ*οο, long-prismatic, parallel or radiating. Cl. basal perfect, ooP and brachydiagonal imperfect; sectile. H. =2 to 2’5; G. =5’5 to 5’7. Steelgrey to dark lead-grey. B. B decrepitates, fuses easily, and wholly volatilizes except a small slag. Sol. in warm n. acid. C.c.: 44’5 lead, with 2 to 4 iron, 34’9 antimony, and 20’6 sulphur. Cornwall, Estremadura, Hungary, Siberia, and Brazil.

223. Dufrenoysite, 2PbS + As 2 S 3 .

Right prismatic. »P 93° 39'. Generally in thick rectangular tables. H. =3; G. =5’56. Lead-grey. Brittle. Binnen, St Gotthard.

224. Frieslebenite, 5(Pb, Ag 2 )S + 2Sb 2 S 8 .

Oblique prismatic, C87° 46'. αP 119° 12'; P o ∞ 31° 41' (fig. 351) in prisms ¼ τ ith curved reed-like faces, and strong vertical striae. Twins intersecting; also massive. Cl. ooP, perfect; fracture conchoidal or uneven; rather brittle. H. = 2 to 2’5; G. =6’2 to 6 ’4. Steel-grey to dark lead-grey. C.c.: 22’5 silver, 32’4 lead, 26’8 antimony, and 18’3 sulphur. Freiberg (Saxony), Hiendelaencina (Spain).

225. Pyrargyrite, 3Ag 2 S + Sb 2 S 3 .

Hexagonal rhombohedral; R (P) 108° 42'; -⅛R137°58'j OR; -2R(r); R3; ooP2(s); and ooR (I). Crystals prismatic (fig. 352); twins common, of various kinds; also massive, dendritic, or investing. Cl. R, rather perfect; fracture conchoidal to uneven and splintery; f ⅛∙ 351 (s P∙ 224). sectile. H. =2 to 2’5. Crimson-red to blackish lead-grey; streak cochineal to cherry-red. Huel Brothers and Huel Duchy in Cornwall, Andreasberg, Freiberg, Johann-Georgenstadt, Annaberg, Schneeberg, Marienberg, Przibram, Schemnitz and Kremnitz, Kongsberg, Mexico, Nevada, &c.

226. Proustite, 3Ag 2 S + As 2 S 3 .

Rhombohedral, like pyrargyrite, except R 107’ 50' (fig. 353).

G. ≈-5 ’ 5 to 5’6. Semitransparent to translucent on the edges. Cochineal to crimson-red. C.c.: 65’5 silver, 15’1 arsenic, and 19’4 sulphur. Streak aurora-red. B. B. arsenical odour, and difficultly reduced to metallic silver. At the same localities as pyrargyrite; both are valuable ores of silver. Red orpiment has a lower specific gravity, and yellow streak; cinnabar volatilizes before the blowpipe.

227. Boulangerite, 3PbS + SbS s .

Fine granular, columnar, radiating, or fibrous; slightly sectile. H. =3; G. =5'8 to 6. Silky, metallic. Blackish lead-grey, with darker streak. B. B. like jamesonite. C.c.: 59 lead, 22’8 antimony, and 18 · 2 sulphur. Molières in France, Oberlahr (Rhenish Prussia), Lapland, and Siberia. Plumbostib or Embrethite, from Nertchinsk, is only a variety.

228. Kobellite, 3PbS, Bi 2 S 8 + 3PbS, Sb 2 S 3 .

Radiated columnar; soft. G. = 6’2to6’3. C. c.: 53 lead, 20 bismuth, 10 antimony, and 17 sulphur. Hvena in Nerike (Sweden).

229. Wittichenite {Cupreous Bismuth), 3CuS + Bi 2 S 3 .

Right prismatic; in tabular crystals like bournonite. Wittichen in the Black Forest.

230. Bournonite (3CuS + Sb 2 S 3 ) + 2(3PbS + Sb 2 S 3 ).

Right prismatic. ooP {d) 93° 40'; f ∞ {n) 96’ 13'; P∞ {e) 92’ 34'; OP (r); ooFoo(s); ooF∞(⅛) (fig. 354). Cl. brachydiagonal, imperfect; fracture uneven to conchoidal; rather brittle. H. =2’5 to 3; G. =5’7 to 5 ’ 9. Lustre brilliant metallic. Steelgrey. C.c.: 42 ’ 4 lead, 13 copper, 25 antimony, and 19’6 sulphur. Redruth and Beeralston; Harz (Neudorf), Braunsdorf, Kapnik, Servoz; Alais and Pontgibaud in France.

Wolchite from Wölch in Carinthia is only a variety.

231. Aikinite {N^eedle-ore), 2(3PbS + Bi 2 S 8 ) + 3(CuS + Bi 2 S 3 ).

Right prismatic; long thin crystals imbedded in quartz, often bent or broken; rather brittle. H. — 2’5; G. =6’7 to 6’8. Blackish lead-grey or steel-grey, with a brownish tarnish. C.c.: 36 lead, 11 copper, 36 bismuth, and 17 sulphur. Berezoff (Siberia), Georgia.

232. Stylotyp, 3(CuAgFe)S + Sb 2 S 3 .

Right prismatic. 0P 92’ 30'. H. =3; G. =4’8. Black. Copiano, Chili. r 1

233. Annivite, 4CuS+ (As 2 S 8 , Sb 2 S 3 , Bi 2 S 3 ).

Massive, similar to the foregoing. From Anniver in Valais. Studerite is similar, but with 15’5 of antimony.

234. Julianite, 3Cu 2 S + As 2 S 3 .

Cubic. G. =5 ’ 12. Metallic. Reddish grey. Rudelstadt in Silesia.

235. Meneghinite, 4PbS + Sb 2 S 3 .

Oblique prismatic, C 72’ 8'. ∞P 140’ 24'; P 0 <x> 70’. Crystals small, acicular, chiefly of ooP c oo, ooP 0 oo, ooP; rare; mostly fibrous. H. — 3; G. — 6 ’4. Bottino in Tuscany, Schwarzenberg in

236. Jordanite, 4PbS + As 2 S 3 .

Right prismatic; ooP 123’ 29'. Cl. brachydiagonal, perfect. Streak black. G. =6’38. C.c.: lead 68’9, arsenic 12'5, sulphur 18 - 6. Binnen and Nagyag.

237. Tetrahedrite {Fahlerz), 4Cu 2 S + Sb 2 S 3 .

Tesseral and tetrahedral. In crystals — , _ —, α >O, — (figs. 2 2 2

855 to 358, also 65, 66, 206). Twins (figs. 164, 207); generally massive. Cl. octahedral; fracture conchoidal; brittle. H. -≈3 ’ 44;

G.-4 ’ 5 to 5’2. Steel-grey to iron-black; streak black (dark red when containing zinc). B.B. on charcoal boils slightly, and fuses to a steel-grey slag, usually magnetic, and with soda gives copper. C.c. essentially Cu 2 S in combination with Sb 2 S 3 . Airthrey near

Stirling, Sandlodge in Shetland, Tomnadashin on Loch Tay, Kirkcudbright; Crinnis and other Cornish mines near St Austell; Harz, Müsen, Freiberg, Camsdorf, Alsace, Kremnitz, and Kapnik. Those with 17 to 31 silver are the Silver Fdhlore (Freiberg). Ore of copper and silver.

238. Tennantite, (CuS, FeS) As 2 S 3 .

Cubic (like fig. 237). Cl. α>O. Brittle. H. =4; G. =4’3 to 4’5. Iron-black; streak dark red, grey. C.c.: 49 copper, 4 iron, 19 arsenic, and 28 sulphur. Redruth and St Day (Cornwall), and Skutterud. Copper-blende, with brownish red streak; G. = 4’3; contains 8 ’9 zinc; Freiberg.

239. Polytelite ( Weissgiltigerz), 4RS + Sb 2 S 8 .

Like tetrahedrite. H. = 2 ’ 5; G. = 5 ’ 4 to 5 ’ 7. C.c.: silver 6 to 22, lead 38 to 52, antimony 8’5 to 22, sulphur 13 to 22’5. Freiberg.

240. Stephanite, 5Ag 2 S + Sb 2 S 8 .

Right prismatic. α>P (o) 115’ 39'; P (P) middle edge 104’ 20'; 2Fao(d) middle edge 107’ 48'; 0P (s); ∞F∞(p) (figs. 333, 334). Cl. d and p, both imperfect; fracture conchoidal or uneven; sectile. H. =2 to 2’5; G. = 6’2 to 6’3. Iron-black to blackish lead-grey. C.c.: 68 ’ 5 silver, 15’3 antimony, and 16 ’ 2 sulphur. Cornwall, Freiberg, Schneeberg, Annaberg, Joachimsthal, Przibram, Schemnitz, Mexico, Peru, and Siberia. Valuable ore of silver.

241. Geocronite, 5PbS + (Sb, As) 2 S 3 .

Right prismatic. Fracture conchoidal; sectile. H. = 2 to 3; G. = 6’45 to 6 - 54. Pale lead-grey. C.c.: 67 lead, with 1 to 2 copper and iron, 16 antimony, with 4’7 arsenic, and 17 sulphur. Sala in Sweden, Meredo (Oviedo) in Spain, and near Pietrosanto in Tuscany.

242. Kilbrickenite, 6PbS + Sb 2 S 3 .

Massive; granular or foliated. C.c.: 70’01 lead, 13’76 antimony, and 16’23 sulphur. County Clare in Ireland.

243. Polybasite, 9(Ag 2 , Cu 2 )S + (Sb, As) 2 S 3 .

Hexagonal; P 117’. Crystals 0P, 00P; and 0P, P, tabular. Cl. basal, imperfect; sectile, and easily frangible. H. = 2 to 2’5; G. = 6 to 6’25. Iron-black, in very thin lamellae, translucent, red. C.c.: 64 to 72 silver, 3 to 10 copper, 16 to 17 sulphur, 0’2 to 8 antimony, and 1 to 6 arsenic. Freiberg, Joachimsthal, Schemnitz, Guanajuato, Nevada, and Idaho. Rich ore of silver.

244. Polyargyrite, 12AgS + Sb 2 S 3 .

Cubic. Typical form O, ooθ∞, αoθ,wιθwι. Cl.cubic. H. =-=2’5; G. = 6’97. Metallic, iron-black; streak black. Malleable. C.c.: 78’2 silver, 7’4 antimony, 14’5 sulphur. Wolfach in Baden.

245. Enargite, 3Cu 2 S + As 2 S 5 .

Right prismatic. Cl. α>P 97’ 53' perfect, brachydiagonal 100’ 58' and macrodiagonal less so. Typical form 00P, 0P, 00P∞, 00F∞. Brittle. H. =3; G. = 4’3 to 4’5. Iron-black. C.c.: 48’3 copper, 19 1 arsenic, and 32’6 sulphur. Morococha in Peru.

246. Clarite, 3CuS + AsS.

Oblique prismatic. Cl. clinodiagonal. Ordinary form 00P, <χ≈P c ∞, OP, mP. H. =3*5; G. =4*46. Dark bluish grey. Kinzig-thal in Baden. Luzonite is similar.

247. Famatinite, 3CuS + SbS.

Right prismatic. Typical form OP, ∞P, ∞Poo, α>P3. Massive or reniform. H. = 3'5; G. = 4 ’ 57. Copper-red to grey; streak black. Famatina Mts. in the Argentine Republic, and Cerro de Pasco in Peru.

248. Chiviatite, 2PbS + 3Bi 2 S 3 .

Foliated, massive. G. = 6 9. Metallic. Lead-grey. Chiviato in Peru.

249. Epigenite, 6RS + As 2 S b .

Right prismatic. ∞P 110° 50 ’. Steel-grey. H. =3 ’ 5. Wittichen.

250. Epiboulangerite, 3PbS + Sb 2 S 6 .

Right prismatic. G. =6*3. Metallic. Blue-black. Altenburg in Silesia.

251. Xanthocon, 2(3AgS + As 2 S 3 ) + (3AgS + As 2 S 5 ).

Hexagonal rhombohedral. R: OR 110° 30'. Crystals thin hexagonal tables; brittle, easily frangible. H. = 2 to 2 ’ 5; G. = 5 to 5’2. Translucent; adamantine. Orange-yellow or brown; streak darker. In the closed tube fuses easily, becomes lead-grey. C.c.: 63 - 4 silver, 147 arsenic, and 21*9 sulphur. Himmelsfürst mine at Freiberg.

252. Pyrostilpnite (Fire-blende}.

Oblique prismatic; crystals like stilbite. OP 139° 12'. Twins on orthodiagonal. H. = 2; G. = 4 - 2. Lustre pearly, and adamantine. Colour hyacinth-red and bright-yellow. Sectile. C.c.: 62*3 silver, with sulphur and antimony. Freiberg, Andreasberg, Przibram.

OXYSULPHURETS.

253. Kermesite, SbO 3 + 2SbS 3 .

Oblique prismatic; crystals ooP∞, OP, acicular and diverging; sectile. H. =1 to 1 ’ 5; G. = 4'5 to 4*6. Translucent; adamantine. Cherry-red; streak similar. Sol. in h. acid. In potash solution becomes yellow, and dissolves. C.c.: 75’3 antimony, 19’8 sulphur, 4 - 9 oxygen. Braunsdorf, Przibram, Pernek near Bösing (Hungary), Allemont, Southham (Canada).

254. Yoltzine, ZnO + 4ZnS.

Incrusting. H. =4*5; G. =3 ’ 7. Yellow. Pontgibaud and Joachimsthal.

255. Karelinite, 3BiO + BiS.

H. = 2; G. = 6*6. Metallic. Lead-grey. Zavodinski in the Altai.

256. Bolivite, Bi 2 O 3 +Bi 2 S 3 .

Rhombohedral. From Bolivia.

SELENITES.

257. Chalcomenite, CuSe + 2H 2 [=CuO, SeO 2 + 2H 2 O].

Oblique prismatic, C 108° 20'. G. =3 - 76. Bright blue. Transparent. C.c.: selenious acid 48 2, copper oxide 35*4, water 15 - 3. Cerro de Cacheuta (Mendoza, Argentine Republic).

NITRATES AND BORATES.

258. Nitratine, Na 2 ⅛ 2 [ = Na 2 O, N 2 O i ],

Rhombohedral; R. 106° 30'. Tarapaca in Peru. Used in the arts as a substitute for nitre; but deliquesces in moist air.

259. Nitre (Saltpetre}, K 2 ⅛ 2 [ = K 2 O, N 2 O 6 ].

Right prismatic. α>P (M} 118° 49'; 2P∞ (P} 70° 55'; P∞ 109° 52'; ooPao(A) (fig. 275); isomorphous with aragonite. Acicular, capillary, or pulverulent. Cl. indistinct; fracture conchoidal. H. = 2; G. = 1 ’ 9 to 2. Semitransparent; vitreous or silky. Colourless, white, or grey. Taste saline and cooling. Deflagrates when placed on hot charcoal; and B. B. on platina wire melts very easily, colouring the flame violet. C.c.: 46'6 potash and 53 4 nitric acid, but always more or less impure. In the limestone caves of many countries; Hungary, Spain, India. Used for producing nitric acid, in glass making, medicine, and the manufacture of gunpowder.

260. Nitrocalcite, CaN 2 + H 2 .

Fibrous or pulverulent. White or grey. C.c.: 30 ’ 8 lime, 59 ’ 3 nitric acid, and 9 - 9 water. Limestone caves of Kentucky; on old walls and limestone rocks.

261. Nitromagnesite, MgN 2 + H 2 .

Taste bitter. In the same places, and similar to nitrocalcite.

262. Boracite, 2Mg 3 B 4 + MgCl.

Tesseral and hemihedral (figs. 63, 253, 359). Cl. octahedral, imperfect; fracture conchoidal; brittle.

H. =7; G. =2’9 to 3. Transparent or translucent; vitreous or adamantine. Colourless or white, often greyish, yellowish, or greenish. Becomes polar electric by heat. B. B. fuses with difficulty to a clear yellowish bead, which on cooling forms a white opaque mass of needle-like crystals; at the same time colours the flame green. Sol. in h. acid. C.c.: 62*5 boracic acid, 26 - 9 magnesia, 7 ’ 9 chlorine, and 27 magnesium. Lüneberg, Segeberg in Holstein, Stassfurt.

263. Stassfurtite.

In very minute prismatic crystals. White. C.c. same as boracite, and thus perhaps dimorphous. Stassfurt.

264. Rhodizite, 2Ca 3 B 4 (?).

H. =8 and G. =3*3 to 3*42; agrees in most characters with boracite. Pyro-electric. Mursinsk in Siberia.

265. Ludwigite, 2MgB + FeFe a .

Fibrous masses. From limestone at Morawitza in the Banat.

266. Borax (Tinkal}, Na 2 2B + 100 2 .

Oblique prismatic, C 73° 25'. ooP 87°; P 122° 34' (fig. 360). Almost isomorphous with augite; brittle. H. =2 to 2·5; G. = 17 to 1 - 8. Pellucid; resinous. Colourless, or yellowish, greenish, and greyish white.

Taste feebly alkaline and sweetish. C.c.: 16 ’ 4 soda, 36*5 boracic acid, and 47’1 v τ ater; but often with 2 phosphoric acid or other impurities. Shores of salt lakes in Tibet and Nepal, in California, and near Potosi.

267. Borocalcite, Ca2B + 6H 2 .

Similar to ulexite (sp. 268); and from same locality.

268. Ulexite, Na 2 2B + 2Ca2B + 18H 2 .

Fibrous. H. =1;G. ≈1*6. White. Tasteless. Iquique and Nova Scotia.

269. Szaibelyite, 2Mg 5 2B + 3H 2 .

H. =3*5; G. =2*7. Werksthal in Hungary.

270. Hydroboracite, 2Ca3B 3 +2Mg3B 3 + 12'H 2 .

Radiating and foliated. Caucasus. A similar mineral, with soda in place of magnesia, is found in Peru.

271. Sussexite, (Mn, Mg) 2 B + H 2 .

Fibrous, silky. White. H. = 3;G. — 3 ’ 4. Franklin (Sussex county, New Jersey).

ANHYDROUS CARBONATES.

272. Calcite (Calc-spar, Calcareous Spar}, CaC.

Hexagonal and rhombohedral; R 105° 5' (fig. 101). The forms and combinations exceed those of any other mineral. Among them are more than fifty rhombohedrons, especially - ⅜R 135°; R; - 2R 79°; and 4R 66°; with OR and ∞R as limiting forms. There are one hundred and fifty-five distinct scalenohedrons, as R3; R2; ∣R3; and the second hexagonal prism ∞P2∙ Hexagonal pyramids are among the rarer forms. Some of the most usual combinations are ∞R, -⅜R (c, ff, fig. 179); or -⅜R, ∞R, very frequent; also ∞R, OR; likewise - 2R, R (f, P, fig. 107); R3, ∞R, - 2R; R5 (y), R3 (r}, R (P}, 4R (m}, α>R (c } (fig. 109); R, R3 (fig. 108). Several hundred distinct combinations are known.

Hemitropes and twins are not uncommon. These occur with the axes parallel (figs. 106, 146, 148, 180, 366, 367). Others are conjoined by a face of R, the axes being almost at right angles, 89° 8' (figs. 183, 369) or by a face of - ⅛R, in which the chief axes form an angle of 127⅛ o ; and usually many times repeated, so that the centre crystals appear in lamellae not thicker than paper (fig. 181); at an obtuse angle, as figs. 149, 363, or an acute angle, as figs. 364, 868. Also occurs granular, lamellar, parallel or radiated fibrous, compact and earthy. Cl. rhombohedral along R, very perfect and easily obtained, so that the conchoidal fracture is rarely observable; brittle. H. —3; G. —2'6 to 2'8; pure transparent crystals=2 72. Pellucid in all degrees. Very distinct double refraction. Lustre vitreous, but several faces resinous, and OR pearly. Most frequently colourless or white, but often grey, blue, green, yellow, red, brown, or black; streak greyish white.

B. B. infusible, but becomes caustic and emits a bright light. Effervesces, and is entirely sol. in h. or n. acid. The fine powder, ignited on platina-foil over the spirit-lamp, forms a somewhat connected mass, and even adheres to the platina. C.c. of the purest varieties, carbonate of lime, with 44 carbonic acid and 56 lime, but usually contains magnesia and protoxide of iron or of manganese. Remarkable specimens of the crystallized variety or proper calc-spar are found at Alston Moor in Cumberland (flat rhombic crystals) and in Derbyshire (pale yellow transparent pyramids), at Strontian, Elie iu Fife (figs. 370, 371, 372), Andreasberg and other parts of the Harz (six-sided prisms), and at Freiberg, Tharand, and Maxen in Saxony.

Certain varieties are distinguished. Iceland Spar, remarkable for its transparency and double refraction, occurs massive and in huge crystals in a trap rock in Iceland. Slate Spar, thin lamellar, often with a shining white pearly lustre and greasy feel; Abergairn and Glen

Tilt in Scotland, Wicklow in Ireland, and Norway. Aphrite, fine scaly; from Hesse and Thuringia. Marble is the massive crystalline variety of this mineral, produced by igneous action on compact limestone. Paros, Naxos, and Tenedos furnished the chief supply to the Grecian artists; Carrara, near the Gulf of Genoa, to those of modem times. Some of the coloured marbles of the ancients were impure limestones, as the Cipollino, zoned with green talc or chlorite and Verde Antique, mixed with green serpentine. Ruin Marble shows irregular markings like ruins; Vai d’Arno (Florentine marble), and Bristol (Cotham marble). Lucullite from Egypt, and Anthraconite, from Campbelltown and Kilkenny, are black from carbon. Lumachello, from Bleiberg in Carinthia, exhibits beautiful iridescent colours from fossil shells, sometimes deep red or orange (Fire Marble). Hislopite, from Poonah, is green, from celadonite.

Limestone occurs in all formations under various names, as Oolite, egg-stone, or roe-stone,—round concretions with a concentric structure like the roe of a fish; Pisolite, or peastone, similar structure; Chalk, soft earthy; Lithographic Stone, yellowish and compact, from Solenhofen; and Marl, calcareous matter more or less mixed with clay. Calcareous Tufa, generally a recent deposit from calcareous springs, has often a loose friable texture, but at other times is hard and compact; and in the neighbourhood of Rome forms the common building stone Travertine. The sandstone of Fontainebleau is carbonate of lime (⅜) mixed with quartz sand (j), and occasionally crystallizing in rhombohedrons.

This mineral is employed in many ways:—the coarser varieties, when burnt to drive off the carbonic acid, as lime, for mortar, manure, tanning; as a flux in melting iron and other ores, or in preparing glass, and for similar purposes; the finer, as marbles, for sculpture, architecture, and ornamental stone-work; the chalk for writing, whitewashing, or producing carbonic acid.

Plumbocalcite.— Cl. 104° 53'. White and pearly; softer than calc-spar; but G. =2'824. Contains 2’3 to 7 ’ 8 carbonate of lead. Wanlockhead and Leadhills (Scotland).

273. Dolomite (Bitter-spar), ÔaC + MgC.

Hexagonal rhombohedral; R 106° 15'-20 ’; most frequent form R. The rhombohedrons often curved and saddle-shaped; also granular or compact, often cellular and porous. Cl. rhombohedral. H. = 3 '5 to 4 '5; G. = 2 85 to 2'95. Translucent; vitreous, but often pearly. Colourless or white, but frequently pale red, yellow, or green. B.B. infusible, but becomes caustic, and often shows traces of iron and manganese. Fragments effervesce very slightly or not at all in hydrochloric acid; the powder is partially soluble, or wholly when heated. C.c.: 54'3 carbonate of lime and 45'7 carbonate of magnesia, but generally carbonate of lime with more than 20 per cent, carbonate of magnesia and less than 20 per cent, carbonate of iron.

Varieties are— Dolomite, massive-granular, easily divisible, white; Rhomb or Bitter-spar, larger grained, or distinctly crystallized and cleavable, often inclining to green; and Brown-spar and Pearl-spar, in simple crystals generally curved (fig. 231), or in imitative forms, of colours inclining to red or brown, more distinct pearly lustre, and under 10 per cent, carbonate of iron. Leadhills and Charlestown in Scotland, Alston in Cumberland, in Derbyshire, Traversella in Piedmont, St Gotthard, Gap in France. Greenish, twinned; Miemo in Tuscany (Miemite), and Tharand in Saxony (Tharandite).

The massive and compact varieties are very common, and are valued as building stones (cathedral of Milan, York Minster, and the Houses of Parliament at Westminster). The Parian marble, and also the Sutherland and Iona marbles, belong to this species.

274. Ankerite, 0aC + (MgFe)C.

R 106° 12'. Usually massive and granular. G. — 2'9to3'l. Otherwise like siderite. Unst (Shetland), Styria.

275. Magnesite, MgC.

Rhombohedral; 107° 10'-30'. Reniform or massive. H. =3'5; G. =2'85 to 2'95. Subtranslucent or opaque; streak shining. Snow-white, greyish or yellowish white, and pale yellow. Tyrol, Norway, North America.

276. Breunnerite (Giobertite), MgC + (MnFe)C.

Hexagonal rhombohedral; R107° 10'-30'. Granular or columnar. Cl. R, very perfect H. =4 to 4'5; G. —2'9 to 3'1. Transparent or translucent on the edges; highly vitreous. Colourless, but often yellowish brown or blackish grey. C.c. essentially carbonate of magnesia, with 517 carbonic acid and 48'3 magnesia, but often mixed with 8 to 17 carbonate of iron or manganese. Unst, Tyrol (in Fassa Valley, &c.), St Gotthard, Harz.

277. Siderite (Sparry Iron, Chalybite), FeC.

Hexagonal and rhombohedral; R 107°. Chiefly R, often curved, saddle-shaped (fig. 232), or lenticular. Cl. rhombohedral along R, perfect; brittle. H. = 3'5 to 4'5; G. — 37 to 3'9. Translucent in various degrees, becoming opaque when weathered; vitreous or pearly. Rarely white, generally yellowish grey or yellowish brom, changing to red or blackish brown on exposure. B.B. infusible, but becomes black and magnetic; with borax and salt of phosphorus shows reaction for iron; with soda often for manganese. In acids soluble with effervescence. C.c. carbonate of iron, with 62 - 1 protoxide of iron and 37’9 carbonic acid, but usually 0'5 to 10 or even 25 protoxide of manganese, 0‘2 to 15 magnesia, and 01 to 2 lime. Unst, Kintyre. In beds or masses in Beeralston in Devonshire, Alston Moor in Cumberland, and in many of the tin-mines in Cornwall, in Styria, Carinthia, and Westphalia; in veins in Anhalt and the Harz; also in the Pyrenees and the Basque provinces of Spain, as near Bilboa; in crystals at Joachimsthal, Freiberg, Klausthal.

Clay Ironstone, grey, blue, brown, or black,—G. =2 , 8 to 3‘5, H. = 3 ’ 5 to 4 - 5, —is an impure variety.

278. Dialogite (Red Manganese), MnC.

Hexagonal rhombohedral; R 106° 56'. Crystals often curved, lenticular, or saddle-shaped; also spherical, reniform, and columnar or granular. Cl. R, perfect. H. = 3 '5 to 4 '5; G. = 3 - 3 to 3 - 6. Translucent; vitreous or pearly. Rose-red to flesh-red; streak white. C.c.: 62 manganese protoxide and 38 carbonic acid. Freiberg, Schemnitz, Kapnik, Nagyag, Elbingerode, and near Sargans.

279. Cobaltspath, CoCo.

Rhombohedral and spheroidal. H. = 4; G. =4 to 4 ’ 13. Peachblossom-red; but dark externally. Schneeberg.

280. Smithsonite (Calamine), ZnC.

Hexagonal rhombohedral; R 107° 40'. Usually reniform, stalactitic, and laminar or granular. Cl. R, perfect, but curved; fracture uneven, conchoidal; brittle. H. =5; G. = 4 ’ 1 to 4'5. Translucent or opaque; pearly or vitreous. Colourless, but often pale greyish yellow, brown, or green. C.c.: 64 - 8 zinc oxide and 35 - 2 carbonic acid. Mendip in Somersetshire, Matlock in Derbyshire, compact at Alston Moor, Chessy near Lyons, Altenberg near Aix-la-Chapelle, Brilon in Westphalia, Tarnowitz in Silesia, Hungary, Siberia.

281. Aragonite, CaC.

Right prismatic. α>P 116° 10'; Poo 108° 26'. The most common combinations are oofoo (h), ooP(3f), Poo (k, P) (fig. 275), generally long prismatic (like the separate crystals in fig. 184); ooPoo, ∞P, 0P, generally short prismatic; crystals of 6P⅜, ∞P, f ∞, 6? ∞ (q) (fig. 373) acute pyramidal. But simple crystals are rare, from the great tendency to form twins, conjoined by a face of »P, and repeated either in linear arrangement (fig. 185) or in rosette grouping (fig. 186). Also columnar, fibrous, and in crusts, stalactites, and other forms. Cl. brachydiagonal, distinct; fracture conchoidal or uneven. H. = 3 - 5 to 4; G. = 2 9 to 3 (massive 2 , 7). Transparent or translucent; vitreous. Colourless, but yellowish white to brick-red; also light green, violet-blue, or grey. In the closed tube, before reaching a red heat, it swells, and falls down into a white coarse powder, evolving a little water. Unst and Leadhills; Valencia, Molina and elsewhere in Aragon; Leogang in Salzburg, and Antiparos. Flos-ferri, coralloid, in the iron-mines of Styria. Satin-spar, fine fibrous silky, at Dufton (Westmoreland). Stalactitic, coast of Galloway, Leadhills, Buckinghamshire, and Devonshire. Also deposited as tufa by the Carlsbad and other hot springs.

282. Witherite, ÈaC.

Right prismatic. α>P (g) 118° 30'; 2P∞(P) 112°. Crystals not common like fig. 275, but generally with quite an hexagonal aspect from being twinned like aragonite (fig. 374). Oftener spherical botryoidal, or reniform, with radiated-columnar structure. Cl. ∞P, distinct; fracture uneven. H. =3 to 3’5; G. = 4 ’ 2 to 4 - 3. Semitransparent or translucent; vitreous, or resinous on the fracture. Colourless, but generally yellowish or greyish. B.B. fuses easily to a transparent globule, opaque when cold; on charcoal boils, becomes caustic and sinks into the support; soluble with effervescence in n. or h. acid. C.c.: 22’3 carbonic acid and 77*7 baryta. Alston Moor and Hexham in Northumberland, also in Styria, Salzburg, Hungary, Sicily, Siberia, and Chili.

283. Alstonite, BaC + 0aC.

Right prismatic. »P 118° 50'; 2P∞ 111° 50'; usual combination P, 2poo, ooP, resembling an hexagonal pyramid (fig. 375). Cl. ooP and ooPco, rather distinct. H. = 4 to 4’5; G. =3 ’ 65 to 3 - 76. 3 ’ 76. Translucent; weak resinous.

Colourless or greyish-white. C.c.: 66 carbonate of baryta and 34 carbonate of lime. Fallowfield near Hexham, and Alston Moor.

284. Strontianite, SrC.

Right prismatic. ooP 117° 19';

Poo 108° 12'. Crystals (fig. 376) and twins like aragonite; also broad columnar and fibrous. Cl. prismatic along oo P (Μ). H. =35; G. =3 - 6 to 3 ’ 8. Translucent or transparent; vitreous or resinous on fracture. Colourless, but often light asparagus-or apple-green, more rarely greyish, yellowish, or brownish. B.B. fuses in a strong heat only on very thin edges, intumesces in cauliflower-like forms, shines brightly, and colours the flame red; easily soluble in acids, with effervescence. C.c.: 30 carbonic acid and 70 strontia, but often contains carbonate of lime (6 to 8).

Strontian in Argyllshire, Sutherland, Leogang in Salzburg, Braunsdorf in Saxony, Hamm in Westphalia, the Harz; at Schoharie (N.Y.) and elsewhere in United States (Emmonite). It is used to produce red fire in pyrotechnic exhibitions.

285. Manganocalcite, (Mn, Ca, Fe) C.

Right prismatic; in prisms like aragonite, and bears the same relation to dialogite that aragonite does to calc-spar. H. = 4 to 5 r G. = 3 '03. Red or reddish white. Vitreous. Schemnitz.

286. Cerussite (Lead Spar), PbC.

Right prismatic; isomorphous with aragonite and nitre. α>P (Μ) 117° 14'; Poo 108° 16'; 2P∞ (u) 69° 20'; also OP; P (0; ⅛Pα> (s); ooP∞ (0; α>P3 (e) (fig 377). Twins common (figs. 158, 159, 378, 379). Also granular or earthy. Cl. ooP and 2P∞, rather distinct; fracture conchoidal; easily frangible. H. = 3 to 3’5; G. — 6 - 4 to 6 - 6. Transparent or translucent; adamantine or resinous. Colourless and often white, but also grey, yellow, brown, black, rarely green, blue, or red; streak white. B. B. decrepitates violently, but easily fused and reduced; soluble with effervescence in n. acid. C.c. . 83’5 protoxide of lead and 16 - 5 carbonic acid.

Very common. Leadhills, Wanlockhead, Keswick, Alston Moor, Beeralston in Devonshire, St Minver in Cornwall; Przibram, Mies, and Bleistadt;

Tarnowitz, Johann-Georgenstadt, Zellerfeld, Klausthal, and many other places.

287. Baryto-Calcite, BaC + CaC.

Oblique prismatic, C 69° 30'. α>P (m) 84° 52', P (s) 106° 54', P 0 oo (ä) 61° (figs. 380, 381); also columnar and granular. Cl. P perfect, P 0 oo less perfect. H. =4; G. — 3 - 6 to 3 , 7. Transparent or translucent; vitreous, inclining to resinous. Yellowish white. C.c.: like alstonite. Alston Moor.

288. Bismuto-sphaerite, Bi a C.

Small fibrous brown concretions from Neustadtel, near Schneeberg.

HYDROUS CARBONATES.

289. Thermonatrite, Na a 0 + H 2 .

Right prismatic. ⅛ (d) 107° 50'; P∞ (o) 83° 50'; with α>Poo (P) in rectangular tables (fig. 382). Cl. brachydiagonal, perfect. H. — 1 ’ 5; G. — 1 5 to 1 ’ 6. Colourless. B.B. like natron, but does not melt. C.c.: 50 ’ 1 soda, 35‘4 carbonic acid, and 14’5 water. Natron lakes of Lagunilla in Venezuela, of Lower Egypt, and of the steppes between Urals and Altai.

290. Natron, Na 2 C + 10H 2 .

Oblique prismatic, C 57° 40'. Crystals artificial; with ∞P 79° 41'; P 76° 28'. Cl. orthodiagonal, distinct. H. = 1 to Γ5; G. —1 ’ 4 to 1 ’ 5. Pellucid; vitreous. Colourless or greyish white. B.B. melts easily, colouring the flame yellow. C.c.: 22 soda, 15 carbonic acid, and 63 water; but mixed with chloride of sodium and other salts. Only as an efflorescence on the ground or rocks (lava of Vesuvius and Etna) in various countries (Hungary, Egypt, Tartary), and in mineral springs and lakes. Used in the manufacture of soap, in dyeing, and in bleaching.

291. Trona, Urao, Na 2 C 3 + 4H 2 .

Oblique prismatic. Crystals 0P (7 ’), ∞P 0 ∞ (Jf), P (n). T: Μ 103° 15' (ng. 383). Cl. orthodiagonal, perfect.

H. =2 ’ 5 to 3; G. =2 ’ 1 to 2’2. Transparent to translucent. Colourless. Does not decompose in the air. Taste alkaline. C. c.: 38 soda, 40 carbonic acid, and 22 water. Fezzan and Barbary ( Trona), Lagunilla (Urao).

292. Gaylussite, Na 2 C + CaC + 5H 2 .

Oblique prismatic, C 78° 27'. Cl. ∞P, imperfect; fracture conchoidal. H. =2 - 5; G. =1 ’ 9 to 1 ’ 95. Transparent; vitreous. Colourless. C.c.: 34 - 5 carbonate of soda, 33 ’ 6 carbonate of lime, 30 - 4 water, with l - 5 clay. Lagunilla.

293. Hydromagnesite, Mg 4 C 3 + 4H 2 .

Oblique prismatic. α>P 88° nearly. Crystals small, rare; also massive. H. =1 ’ 5 to 3; G. =2 - 14 to 2 ’ 18. Vitreous or silky. White. C.c.: 36 ’ 2 carbonic acid, 44 magnesia, and 19’8 water. Unst (Shetland), Moravia, Kumi in Negropont, Hoboken in New Jersey, and Texas in Pennsylvania.

294. Azurite (Blue Copper), Cu 8 C 2 +Π 2 .

Oblique prismatic, C 87° 39'. ∞P (Μ) 99° 32';-P (k') 106° 14'. Crystals 0P, ooP, α>P o o o,-P (or h, Μ, s,k', in fig. 384, but in another position); also radiated and earthy. Cl. clinodomatic (P) 59° 14', rather perfect; fracture conchoidal or splintery.

H.-3∙5 to 4 2; G.-37 to 3 8. Translucent or opaque; vitreous. Azure-blue, the earthy varieties (and streak) smaltblue. B.B. on charcoal fuses and yields a grain of copper; soluble with effervescence in acids, and also in ammonia. C.c.: 691 protoxide of copper, 25 ’ 7 carbonic acid, and 5'2 water. Crystals at Redruth, Alston Moor, Chessy near Lyons, in Siberia, Moldawa in the Banat, Burra-Burra (Australia). Valued as an ore of copper.

295. Malachite, 0u a C + H a .

Oblique prismatic, C 61° 50'. ∞P 104° 20'. Crystals α>P (Λf), ∞P 0 oo (s), 0P (P), in hemitropes (fig. 385). In general acicular, scaly, or reniform, stalactitic, and radiated fibrous. Cl. basal and clinodiagonal, very perfect. H. = 3 '5 to 4; G. =3 - 6 to 4. Transparent or translucent on the edges; adamantine, vitreous, silky, or dull. Emerald and other shades of green; streak applegreen. B.B. and with* acids like azurite. C.c.: 71 '8 copper protoxide ( = 57 - 5 copper), 20 carbonic acid, and 8’2 water. Crystalline at Rheinbreitenbach on the Rhine and Zellerfeld in the Harz; fibrous and compact at Sandlodge in Shetland, Leadhills, Cornwall, Wales, and Ireland, at Chessy in France, Siberia, the Urals, Saalfeld in

Thuringia, Moldawa in the Banat, in North America, Africa, and Australia. Frequently pseudomorphous after copper and its ores, also after calcite and cerussite. Valuable ore of copper; the finer varieties are prized for ornamental purposes.

296. Hydrozincite, ZnC + 2ZnH 2 .

Massive. C.c.: zinc oxide 75 - 3, carbonic acid 13 - 6, water 11 1. Spain, Westphalia, Bavaria, Persia, United States. Valuable ore.

297. Aurichalcite, 2CuC + 3ZnH a .

Acicular. H. ≈2. Translucent, pearly, and verdigris-green. C.c.: 29 - 2 copper protoxide, 44 ’ 7 zinc oxide, 16’2 carbonic acid, and 9 - 9 water. Leadhills, Matlock, Loktevski in the Altai.

298. Emerald-Nickel (Zaratite), l⅛iC + 6H 2 .

Amorphous, reniform, and incrusting. H. =3; G. —2 ’ 6to2∙7. Translucent; vitreous. Emerald-green. C.c.: 59 - 3 nickel protoxide, 11 ‘7 carbonic acid, and 29 water. On chromite at Hagdale in Unst, Texas in Pennsylvania; also Cape Ortegal in Spain, Tyrol, and Ekaterinburg in the Urals.

299. Lindakerite, Ü 2 C + 2CaC + 10H 2 .

In small siskin-green crystalline aggregates. H. = 2 ’ 5 to 3. From Elias mine near Joachimsthal, implanted on pitch-blende.

300. Voglite, 4UC + 7CaC + 30uC + 24H 2 .

Rhomboidal. Emerald-green scales with pearly lustre. Elias mine, Joachimsthal.

301. Liebigite, U 2 C + 0aC + 20H 2 .

Mammillary concretions. H. =2 to 2’5. Apple-green. Adrianople, Joachimsthal, and Johann-Georgenstadt.

302. Bismuthite, Bi 4 C 3 + 4H 2 .

Disseminated, investing or acicular; fracture conchoidal or uneven; very brittle. H. =4 to 4 ’ 5; G. =6‘8 to 6'91. Opaque; dull vitreous. Grey, yellow, or green. C.c.: 90 ’ 1 bismuth oxide, 6 ’ 4 carbonic acid, and 3 - 5 water. Ullersreuth (Reuss), Schneeberg, Johann-Georgenstadt; also Chesterfield in South Carolina.

303. Lanthanite, LaC + 3∏,.

Right prismatic. α>P 92° 46'. Small tabular crystals; usually granular or earthy. Cl. basal. H. =2; G. = 2 ’ 7. Dull or pearly. White or yellowish. C.c.: 21 carbonic acid, 55 lanthanum oxide, and 24 water. Bastnaes in Sweden, Lehigh in Pennsylvania.

CARBONATES WITH HALOID SALTS, &c.

304. Phosgenite, PbCl + PbC.

Pyramidal. P 113° 56'. Crystals short-prismatic or sharp-pyramidal. Cl. oo P, rather perfect; fracture conchoidal. H. =2 ’ 5 to 3; G. = 6 to 6 ’ 2. Transparent or translucent; resinous adamantine. White, yellow, green, or grey. C.c.: 51 chloride and 49 carbonate of lead. Very rare. Stottfield near Elgin in Scotland, Matlock and Cromford in Derbyshire, Tarnowitz.

305. Parisite, 3CeC + CaF.

Hexagonal. Ρ 164° 58'. Cl. basal, perfect. H. = 45; G. = 4 35. Vitreous; on cleavage - plane pearly. Brownish yellow, inclining to red. C.c.: 23’5 carbonic acid, 42 5 protoxide of cerium, 8 ’ 2 lanthanum oxide, 9 - 6 didymium oxide, 2 ’ 8 lime, 10 Ί fluoride of calcium, and 2'2 fluoride of cerium. Emerald mines of the Muzo Valley in Colombia, Urals.

306. Leadhillite (Jfaxιte), Pb 18 C 9 S 8 O 51 + 5H 2 .

Right prismatic. P middle edge 137°; ∞P 120° 20'; 2p∞ 43 β 12'.

Mostly tabular; also twins. Cl. basal, perfect; slightly brittle. H. =2 - 5; G. =6 - 26 to 6’44. Transparent or transluce·t; resinous or adamantine, pearly on OP. Yellowish white, inclining to grey, green, yellow, or brown. C.c.: 81’98 oxide of lead, 8’03 carbonic acid, 8 ’ 12 sulphuric acid, 1∙8 water. Leadhills, Taunton, Nertchinsk, Granada. Maxite from Sardinia.

307. Susannite, 3PbC

+ PbS.

Rhombohedral; R 72° 29'. Cl. basal, perfect. H.-2’5; G. =6∙55. White, green, yellow, brownish. Resinous to adamantine; pearly on the cleavage faces. Powder white. C.c.: 72 ∙5 carbonate and 27’5 sulphate of lead. From the Susanna mine at 3

Leadhιlls, but very rare; s p '' s vp ,, also in large dark crystals from the Banat.

ANHYDROUS SULPHATES.

308. Arcanite {Glaserite), K 2 S.

Right prismatic. Acute pyramids, with o°P 120° 24'; dimorphous and also rhombohedral, with R 88° 14'. Mostly in crusts, or pulverulent. Cl. basal, imperfect. H. = 2’5 to 3; G. =2’7. Pellucid; vitreous or resinous. Colourless or white. C.c.: 54 potash and 46 sulphuric acid. Lavas of Vesuvius and other volcanoes.

309. Mascagnine, (NH 4 ) 2 S.

Right prismatic. 00P 121° 8'; but chiefly in crusts and stalactites. Cl. perfect; sectile. H. =2 to 2’5; G. — l’7tol’8. Pellucid; vitreous. Colourless, white, or yellowish. Taste pungent and bitter. C.c.: 25’9 ammonia, 60 5 sulphuric acid, and 13 6 water. Near volcanoes, as Etna, Vesuvius, the Solfatara, the Lipari Islands, in the marshes near Siena, and in ignited coal-beds, as at Bradley in Staffordshire.

310. Thenardite, Na a S.

Right prismatic. Acute pyramids P, with 0P and 00P, in crusts and druses. Cl. basal, perfect; fracture uneven. H. = 2’5; G. = 2’6 to 2 ’ 7. Pellucid; vitreous. White. C.c.: 43’82 soda and 56’18 sulphuric acid. In salt deposits near Aranjuez (Spain) and at Tarapaca (Peru)

311. Glauberite {Brongniartine), Na 2 S + 0aS.

Oblique prismatic, C 68° 16'. 0P, - P, or with 00P (P, f t Μ, fig. 392). Cl. basal, perfect; along 00 Ptraces. H. =2’5 to 3; G. ≈=2 - 75 to 2 - 85. Translucent; vitreous to resinous. Colourless. C.c.: 51 sulphate of soda, and 49 sulphate of lime. Villarubia in Spain, Vic, Berchtesgaden, near Brugg in Aargau, Aussee and Ischl in Austria; Tarapaca in Pera, with 1 to 5 boracic acid.

312. Anhydrite {Karstenite), CaS.

Right prismatic. 00P 90° 4'. Chiefly granular, or almost compact or columnar. Twins rare. Cl. macrodiagonal and brachydiagonal, both perfect; basal perfect. H. =3 to 3’5; G. =2’8 to 3. Transparent or translucent; vitreous; on 00P∞ pearly. Colourless or white, but often blue, red, or grey; streak greyish white. C.c.: 58’75 sulphuric acid and 41’25 lime.

The crystalline, or Muriacite, occurs in the salt-mines of Bex, Hall in Tyrol, and Aussee in Styria, also at Sulz, Stassfurt, and Bleiberg. Compact at Ischl in Austria, Berchtesgaden, Eisleben, and the Harz. Granular, or Vulpinite, near Bergamo. The contorted, or Gekrösstein, chiefly at Wieliczka and Bochnia.

313. Baryte {Heavy Spar), BaS.

Right prismatic. P∞ {g) 78° 20'; f□o {f) 105° 22'; oof2 {d) 77° 44'; also 00P∞ (c) (figs. 125, 126, 127, but in a different position, d, d being placed vertical). The crystals show very many forms and combinations, and are tabular or columnar, often in druses or groups; also foliated, fibrous, granular, or compact. Cl. brachydiagonal perfect, along f∞ less perfect; basal, traces. H.=3 to 3’5; G. = 4’3 to 4’7. Transparent to translucent; vitreous or resinous. Colourless and white, but generally reddish white, or flesh-red, yellow, grey, bluish, greenish, or brown. B.B. decrepitates violently, and fuses very difficultly, or only on the edges, colouring the flame yellowish green; not soluble in acids. C.c.: 34’3 sulphuric acid and 65’7 baryta, but occasionally with 1 to 15 sulphate of strontia. Very common, chiefly in veins, either alone or accompanying ores. Crystals at Arran, Strontian, Elie, Sutherland; Dufton, Bohemia, Felsöbanya and Kremnitz in Hungary, Auvergne, and United States. Columnar at Freiberg. The radiated from near Bologna, or the Bolognese Stone, phosphoresces in the dark. Massive, or Cawk, from Derbyshire and Staffordshire, Leadhills, and Arran.

Lime Barytes, from Derbyshire, Strontian, Freiberg, seems a mixture with sulphate of lime; crystals tabular, in rosettes and other groups; G. = 4 to 4’3. Hepatite, dark grey, from carbonaceous matter; Kongsberg. Allomorphite, scaly, white, and pearly, near Rudolstadt, agrees essentially with barytes.

314. Baryto-Celestine, 2SrS + BaS .

Radiated and foliated. Bluish white. Brittle and friable. H. = 2 ’5; G. = 3 ’92. Difficultly fusible. Lake Erie, Upper Canada, and Biunenthal.

315. Celestine, Sr’S.

Right prismatic; forms like barytes and anglesite. P∞ (0) 104° 8'; Poo {M) 75° 58'. Usual combinations P∞ , P∞, ∞P∞; or this with ooP2 {d); also columnar and foliated; or fibrous, fine granular, or compact. Cl. macrodiagonal, perfect; along P∞ less perfect. H. =3 to 3’5; G. =3’9 to 4. Transparent or translucent; vitreous or resinous. Colourless, but usually bluish white to indigo-blue, and rarely reddish or yellowish. B.B. decrepitates and fuses easily to a milk-white globule; colours the flame carmine-red. Distinguished from barytes by a splinter, after ignition in the inner flame, on being moistened with h. acid, and held in the blue border of the flame of a candle, colouring this of a lively purple-red. Scarcely affected by acids. C.c.: 43’6 sulphuric acid and 56’4 strontia, but often some baryta or lime. Tantallon Castle, Calton Hill, Clachnaharry; near Bristol and Knaresborough; sulphur-mines of Girgenti and other parts of Sicily, Herrengrund in Hungary, Bex, Salzburg, Monte Viale near Verona, and Meudon and Montmartre near Paris. Used for producing a red light in pyrotechnic mixtures.

316. Anglesite, PbS.

Right prismatic. 00P 103° 43'; P∞ 75° 35'. The crystals, of many forms and combinations, are short prismatic, pyramidal, or tabular. Cl. prismatic along ∞P, and basal; fracture conchoidal; very brittle. H. =3; G. =6’2 to 6’35. Transparent or translucent; adamantine or resinous. Colourless and white, but occasionally yellow, grey, brown, or blue; streak white. Decrepitates in candle;

B.B. on charcoal fuses in the oxygen flame to a milk-white bead; very difficultly soluble in acids, wholly in solution of potash. C.c.: 73’7 lead protoxide and 26’3 sulphuric acid. Leadhills (fig. 397), St Ives in Cornwall, Derbyshire, Parys mine in Anglesea, Zellerfeld, Klausthal, Badenweiler, Siegen, Silesia, Linares, Phoenixville in Pennsylvania.

317. Lanarkite, PbS + Pb.

Oblique prismatic. ∞P49° 50'. Cl. basal, perfect; sectile; thin laminae flexible. H. =2 to 2’5; G. =6’3 to 6’7. Transparent; resinous or adamantine; on 0P pearly. Greenish or yellowish white, inclining to grey; streak white. B. B. on charcoal fuses to a white globule containing metallic lead; partially soluble in n.

acid with effervescence. C.c.: sulphate of lead 57'6, oxide of lead 42 *4. Leadhills; rare.

HYDROUS SULPHATES.

318. Mirabilite {Glauber Salt), Na a S + 10H 2 .

Oblique prismatic, C 72° 15'. Cl. orthodiagonal; fracture conchoidal. H. = 1*5 to 2; G. ∙=l*4to 1*5. Pellucid and colourless. C.c.: 19 ’ 2 soda, 24 8 sulphuric acid, and 56 water. As an efflorescence in quarries, on old walls, or on the ground; in the waters of lakes and springs in Russia and Egypt, and on Vesuvius on lava.

319. Gypsum, C⅛S + 2H 2 .

Oblique prismatic, C 80’ 57'. The most common forms are ooP 11 l o 30'; P 138° 40'; - P 143° 30'; and ∞P c ∞. Two common combinations are α>P(∕), ooP c oo (p), - P (I) (fig. 129), and this with P. Lenticular crystals often occur; hemitropes frequent (figs. 161,150, 151); also granular, compact, fibrous, scaly, or pulverulent. Cl. clinodiagonal perfect, along P much less perfect; sectile; thin plates flexible. H. =1*5 to 2 (lowest on P); G. =2*2 to 2*4. Transparent or translucent; vitreous, on cleavage pearly or silky. Colourless, and snow-white, but often red, grey, yellow, brown, and more rarely greenish or bluish. In the closed tube yields water. B.B. becomes opaque and white; soluble in 400 to 500 parts of water, scarcely more so in acids. C.c.: 46'5 sulphuric acid, 32*6 lime, and 20*9 water.

Transparent crystals, or Selenite, occur in the salt-mines of Bex in Switzerland, of the Tyrol, Salzburg, and Bohemia, in the sulphur-mines of Sicily, at Lockport in New York, in porphyry at Gourock, in the clay of Shotover Hill near Oxford, at Chatley near Bath, and many other localities. Fibrous gypsum at Campsie, Matlock in Derbyshire, and at ∏feld in the Harz. Compact gypsum in whole beds in many parts of England, Germany, France, and Italy, at Volterra in Tuscany (Alabaster) often with rock-salt. The finer qualities (or alabaster) are cut into various ornamental articles.

320. Kieserite, MgS + H 2 .

Rhombic, but chiefly massive. G. =2*52. Pellucid; greyish white. C.c.: magnesia 29, sulphuric acid 58, water 13. In beds at Stassfurt.

321. Epsomite (Epsom Salt), MgS + 7ft 2 .

Right prismatic. P mostly hemihedric; ooP 90’ 38'. ∞P (Μ), oofαo (o), P (I) (fig. 399). Granular, fibrous, or earthy. Cl. brachydiagonal, perfect. H. =2 to 2’5;

G. =1*75. Pellucid; vitreous; and white. Taste bitter. C.c.: 16*32 magnesia, 32*53 sulphuric acid, and 51Ί 5 water. Efflorescence on various rocks, as at Hurlet near Paisley, Idria, Montmartre, and Freiberg; on the ground in Spain and the Russian steppes; in mineral waters, as at Epsom in Surrey, Saidschitz and Seidlitz in Bohemia. Used in medicine.

322. Goslarite (White Vitriol), ZnS + 7H 2 .

Right prismatic. ooP 90° 42'; isomorphous with epsomite. ooP, oof oo, P (if, o, I) (fig. 399). Mostly granular or stalaetitic; * 1 g∙ 399 (s P∙ 321 X reniform and incrusting. Cl. brachydiagonal, perfect H. =2 to 2*5; G. =2 to 2*1. Pellucid; vitreous. White, inclining to grey, yellow, green, or red. Taste nauseous-astringent. C.c.: 28*2 zinc oxide, 27*9 sulphuric acid, and 43 *9 water. Holywell in Flintshire, Cornwall, Ram-τnelsberg near Goslar in the Harz, Falun, Schemnitz. Used in dyeing and medicine.

323. Morenosite, NiS + 7H 2 .

Acicular, fibrous, and as an efflorescence. H. =2 to 2*25; G. =2. Lustre vitreous. Apple-green; streak white. Soluble. Mor-verιι in Argyllshire, Cape Ortegal (Spain), Lake Huron, Pennsylvania.

324. Melanterite (Green Vitriol, Cop peras), FeS + 7H 2 .

Oblique prismatic, C 75° 45'. ooP (f) 82° 22'; - P (P) 101° 34'; P β <≈o (o) 67° 30' (fig. 400); chiefly stalaetitic, reniform, or in crusts. Cl. basal, perfect; prismatic less so. H. = 2; G∙ = 1 *8 to 1 *9. Translucent, rarely transparent; vitreous. Leek-ormountain-green, often with a yellowish coating; streak white. C.c.: 26 protoxide of iron, 29 sulphuric acid, and 45 water. Hurlet near Paisley, Bodenmais, Rammelsberg, Falun, Schemnitz, Bilin. Used in dyeing, and in manufacturing ink, Prussian blue, and sulphuric acid.

325. Smikite, Mn 2 S + H 2 .

Stalaetitic aggregates. Rose to white. Felsöbanya (Hungary).

326. Mallardite, MnS + 7H 2 .

Crystalline foliated masses; apparently oblique prismatic. Lucky Bay mine in Utah.

327. Bieberite (Cobalt Vitriol), CoS + 7H 2 .

Oblique prismatic; usually stalaetitic, or an efflorescence. Pale rose-red. C.c.: 20 cobalt oxide, 4 magnesia, 29 sulphuric acid, and 47 water. Bieber near Hanau, and Leogang.

328. Alunogene (Hair-Salt), A1 2 S + 180 2 .

Capillary or acicular, in crusts or reniform masses. H. —1*5 to 2; G. = 1 *6 to 1 *7. Silky. White, inclining to green or yellow. C.c.: 36 sulphuric acid, 15*4 alumina, 48*6 water. Volcanoes of South America, in coal and lignite in Germany, and on old walls.

329. Aluminite ( Websterite), AL 2 S + 9H.

Reniform, and very fine scaly, or fibrous. Fracture earthy; sectile or friable. H. = 1; G. — 1 *7. Opaque; dull or glimmering; snow-white or yellowish white. C.c.: 29*8 alumina, 23*2 sulphuric acid, and 47 water. Newhaven in Sussex; Epernay, Auteuu, and Lunel Vieil in France; Halle and Morl in Prussia. Felsöbanyite, from Hungary, in rhombic tubes, is similar, but has 10 per cent, of water.

330. Coquimbite, Fe 2 3S + 9H 2 .

Hexagonal. P 58°. Crystals 0P; with α>P and P; usually granular. Cl. ooP, imperfect. H. =2 to 2*5; G.— 2 to 2 1. White, also brown, yellow, red, and blue. C.c.: 28*5 iron peroxide, 42*6 sulphuric acid, and 28*9 water. Copiapo in Chili, and Calama in Bolivia.

331. Copiapite, 2F⅛ 2 5S + 13H 2 .

Six-sided tables, but system uncertain; also granular. Cl. perfect. Translucent; pearly. Yellow. C.c.: 34 iron peroxide, 42 sulphuric acid, and 24 water. Copiapo in Chili. Also radiated-fibrous masses, dirty greenish yellow, incrusting the former, with 32 sulphuric acid and 37 water. Both probably mixtures.

Fibroferrite, also from Chili, and Yellow Iron Ore, from the brown coal at Kolosoruk in Bohemia and Modum in Norway, are both reniform, or compact and earthy. H. = 2*5 to 3; G. —2*7 to 2*9. Colour ochre-yellow. Apatelιte, reniform-earthy, yellow, from Auteuil near Paris, is similar; also Vitriol Ochre from Falun. Misy, from Rammelsberg in the Harz, containing sulphates of iron, copper, zinc, and other metals, is a product of decomposition.

332. Pissophane, (Al 2 Fe 2 ) 2 S + 15H 2 .

Stalaetitic; fracture conchoidal; very easily frangible. H. — 2; G. = 1 *9 to 2. Transparent or translucent; vitreous. Olive-green to liver-brown; streak greenish white to pale yellow. C.c.: 7 to 35 alumina, 10 to 40 iron peroxide, 12 sulphuric acid, and 41 water. Saalfeld and Reichenbach in Saxony.

Carphosiderite, reniform, opaque, resinous, and straw-yellow, with a greasy feel, is related. H. = 4 *5; G. = 2*5. Consists of hydrous sulphate of iron. Labrador.

333. Chalcanthite, (5uS + 50 2 .

Anorthic. coPoo (n): α>Poo (r) 79’ 19'. P' (P)∙. α>P ’ (T) 127’ 40'. P: n 120° 50'. P: r 103° 27'. α>P' (T): oo'P (Μ) 123° 10' (fig. 401). Generally incrusting. Cl. T and Μ, imperfect. H. = 2*5; G.=2*2. Blue. C.c.: 32 protoxide of copper, 32 sulphuric acid, 36 water. Cornwall, Wicklow, Hungary, Tyrol, Falun, and on lava of Vesuvius.

334. Brochantite, CuS + 30uH 2 .

Right prismatic. ooP 104’ 32'; i ’ <n 152° 37'; and α>fα>; also reniform. Cl. brachydiagonal, perfect. H. -= 3*5 to 4; G. =3*75 to 3 9. Transparent or translucent; vitreous. Emerald or blackish green; streak bright green. C.c.: 70 copper protoxide, 18 sulphuric acid, and 12 water. Sandlodge (Unst), Roughton Gill in Cumberland, Rezbanya, Ekaterinburg; also Krisuvig in Iceland (Krisuvigite).

335. Langite, CuS + 3CuH 2 + 2H 2 .

Eight prismatic. 00P 123° 44'. Crystals long-tabular, mostly in twins. Also in fibro-lamellar and concretionary crusts, with earthy surface. Cl. basal and brachydiagonal. H. = 2 ’5; G. = 3’5. Vitreous. Greenish blue. C.c.: 65’1 copper protoxide, 16’4 sulphuric acid, and 18’5 water. Cornwall.

War ring tonite is similar; also Konigine from Siberia.

336. Johannite (Uran-vitriol).

Oblique prismatic, C 85° 40'. ∞P 69°. Crystals similar to trona (No. 291, fig. 383), but minute; arranged in concretionary and reniform masses. H. =2 to 2’5; G. = 3’19. Semitransparent; vitreous. Soluble. Taste bitter. Bright grass-green. C.c.: oxides of uranium 6772, oxide of copper 5’99, sulphuric acid 20’02, water 5 ’ 59. Joachimsthal (Bohemia), Johann-Georgenstadt.

337. Blödite (Astrakanite), (MgNa 2 )S + 2H 2 .

Oblique prismatic, C 100° 43'. ooP 0 2 112° 55'; α>P (∞), ∞P c oo (δ), ∞P 0 2 (n), ooP 0 oo (a), -Pfp), P c ∞ (d), OP (c) (fig. 403). In prismatic crystals, or efflorescent. H. = 3 ’5; G. = 2 ’ 2. Transparent. White or red.

C.c.: 47’9 sulphuric acid, 8’5 soda, 12 magnesia, and 21 5 water. Salt lakes on the Volga near Astrakhan, Ischl, Stassfurt, and near Mendoza in South America.

Reussine from Seidlitz is similar, but a mixture.

338. LowEiTE,2(Na 2 S + MgS) + 5H 2 .

Pyramidal, but only compact. Cl. basal, distinct; also octahedral, with angles 110° 44' and 105° 2'. H. =2’5 to 3; G. =2’376. Vitreous. Yellowish white to flesh-red. C.c.: 20 soda, 13 magnesia, 52 sulphuric acid, and 15 water. Ischl.

339. Syngenite, K 2 S + CaS + ¾.

Oblique prismatic, C 76°. ∞P 73° 55'. Crystals ooP 0 oo (a), <x>P c ∞ (δ), 0P (c), oo P (p), ooP o 2 (j>"), ooP°3 (p ’ "), 2P 0 2 (e'), P (o'), 2P (o"), P c ∞ (2 )-P 0 ∞ (r), P o ∞ (r'), 2P 0 oo (√'), -∣P 0 ∞ (e). Cl. ooP, perfect; fracture conchoidal. H. =2’5; G. =2’25. Colourless to milk-white. C.c.: lime 16 ’ 88, potash 28’55, sulphuric acid 48’45, water 5’47. Soluble in 400 parts of water. In cavities in halite at Kalusz (Galicia).

340. Polyhalite, 2CaS + MgS + K 2 S + 2⅛.

Right prismatic. ooP 115°. Mostly fibrous. H. = 3 ’ 5; G. = 2 7 to 2 ’ 8. Translucent; resinous. Colourless, generally brick-red. C.c.: sulphate of lime 45, of magnesia 20’5, of potash 29, water 5’5. Ischl, Aussee, and Berchtesgaden.

341. Alum, RS + (Al 2 Fe 2 jS 3 + 24H 2 .

Cubic. 0, sometimes with ∞O∞ and O∞. Generally efflorescent in fibrous crusts. Cl. octahedral; fracture conchoidal. H. =2 to 2’5; G. = 175 to 1 ’9. Translucent. White. Taste sweetish-astringent. Soluble. B. B. evolves sulphurous fumes, (a) Potash Al·um: RO = K 2 O; 337 sulphuric acid, 10’9 alumina, 9’9 potash, and 45’5 water. In the coal formation at Hurlet and Campsie in Scotland; the Tertiary brown coals of Hesse and the Rhine; the Lias near Whitby; Silurian alum slates of Scotland, Norway, and Sweden; the volcanic formations of the Lipari Islands, Sicily, and the Azores, (δ) Ammonia Alum: RO = (NH 4 O) 2 ; about 4 per cent, oxide of ammonium and 48 water. In closed tube forms a sublimate of sulphate of ammonia. Tschermig in Bohemia. (c) Soda Alum: RO = Na 2 O; with 7 of soda and 48 water. Mendoza in South America, Solfatara near Naples, and Milo, (d) Magnesia Alum: RO = MgO. Translucent and silky. South Africa, Iquique in Peru (Pickeringite'), (e) Iron Alum (Feather Alum) : RO = FeO. Hurlet near Paisley, Mörsfeld in Bavaria, Krisuvig in Iceland, (f) Manganese Alum: RO = MnO. From Delagoa Bay in South Africa. An alum with 37 oxide of zinc occurs at Felsöbanya, and has been termed Dietrichite.

342. Voltaite, 3(Fe, K 2 )S + 2(Fe 2 Al 2 )S + 12H 2 .

Cubic. 0; ∞O∞; O∞. Black, brown, or green. H. = 3; G. = 279. Solfatara near Naples, Goslar in the Harz, and Kremnitz.

343. Alunite, K 2 S + 3A1 2 S + 6H 2 .

Rhombohedral; R 89° 10'. Crystals R and OR (fig. 405); also earthy. Cl. basal. H. =3’5 to 4;

G. =2’6 to 2’8. Translucent; vitreous, pearly on O. Colourless, but often stained. Hungary, Tolfa (near Ci vita Vecchia), Lipari Islands, Auvergne, and Milo.

344. Jarosite, ⅛ 2 S + Fe 2 3S +

2(Fe 2 3H 2 ).

Rhombohedral; R 88° 58'. Cl. basal; also fibrous in nodules or incrusting. H. = 2’5 to 3’5; G. = 3’24. Colour ochre-yellow. Spain, Saxony, and Mexico.

345. Gelbeisenerz, K 2 S + 4Fe 2 S + 9H 2 .

Foliated and massive. H. =2’5 to 3; G. = 27 to 2’9. Bohemia, Norway, and Tcheleken Island in the Caspian Sea.

346. Urusite, Fe 2 S + 2Na 2 3S + 8H 2 .

Tcheleken Island in the Caspian.

347. Botryogene (Red Vitriol), Fe 3 S 2 + 3(Fe 2 2S) + 36H 2 .

Oblique prismatic, C 62° 26'. ∞P 119° 56'. Commonly botryoidal. H. = 2 to 2 ’5; G. = 2. Translucent; vitreous. Hyacinth-red and orange-yellow. Falun in Sweden.

348. Herrengrundite.

Oblique prismatic, C 88° 50'. Dark emerald-green crystals. H.=2’5; G. = 3’13. C.c.: 57’22 oxide of copper, 23 04 sulphuric oxide, 19 ’44 water, sometimes with lime. Heιτengrund (Hungary).

349. Linarite, (PbS + II 2 Pb) + (0uS + ⅛ 2 Cu).

Oblique prismatic, C 77° 22'. ∞P (Μ) 61° 41'; 2P 0 ∞ (tt ) 52° 31'. Crystals ∞P 0 ∞ (a), OP (c), and the above forms generally. Hemitropes united by <χP 0 ∞ (a). Cl. orthodiagonal, perfect; fracture conchoidal. H. = 2 ’5 to 3; G. = 5 ’ 2 to 5 ’45. Translucent; adamantine. Azure-blue to dark blue; streak pale blue. C. c.: oxide of lead 55’69, oxide of copper 19’83, sulphuric acid 19’98, water 4’5. Leadhills, Red Gill and Roughton Gill (Cumberland), Linares in Spain, and Nertchinsk.

350. Caledonite, 5PbS + 2(H 2 Pb) + 3(H 2 0u).

Right prismatic. α>P (m) 95°;P«> (e) 70° 57'; 2P∞ (χ) 36° 10'. Crystals frequently as in fig. 407, but generally hemihedral. Cl. brachydiagonal, a distinct; m, c imperfect. H. = 2 , 5 to 3; G. = 6 ’ 4. Transparent; resinous. Verdigris-green and mountain-green; streak greenish white. C.c.: 68’42 oxide of lead, 10’17 oxide of copper, 17’3 sulphuric acid, 4Ό5 water. Leadhills, Red Gill in Cumberland, Rezbanya in Transylvania.

351. Lettsomite, 3Cu 3 S + 2(A1 2 3H 2 ) + 15H 2 .

Right prismatic; but in tufts of capillary crystals with velvet-like appearance. Colour smalt-blue to sky-blue. C.c.: 49 oxide of copper, 2’97 lime, 11’21 alumina, 1’41 oxide of iron, 12 Ί sulphuric acid, 22’5 water. Moldawa in the Banat. Woodwardite is probably an aluminous variety of the above. Turquoise-blue to greenish blue. Cornwall.

352. Kainite, MgS + KC1

+ 3H 2 .

Oblique prismatic, C 85° 5' (fig. 408). G. =2’13. Cl. orthodiagonal. White to reddish.

C.c.: 16Ί magnesia, 157 potash, 32’2 sulphuric acid, 14’3 chlorine, 217 water. Stassfurt.

TELLURATES AND CHROMATES.

353. Montanite, Bi 2 Te + 2H 2 .

lncrusting, earthy. Lustre waxy. Yellowish. Opaque. C.c. bismuth 66 , 8, tellurium 26'8, water 5'9. Highland in Montana.

354. Magnolite, ÉgTe.

"White acicular crystals from Keystone mine in Colorado.

355. Crocoisite, RbCr.

Oblique prismatic, C 77° 27'. ∞P 93° 42' (MY - P 119°12' (t), ∞P e 2 (∕) 56° 10', ooP<≈∞ (g), (fig. 409).

Cl. oo P, distinct; sectile. H. =2'5to 3; G. =5 , 9to6Ι. Translucent; adamantine. Hyacinth-or aurora-red; streak orange-yellow. C.c.: 31 chromic acid, and 69 lead protoxide. Berezoff, Mursinsk, and Nijni-Tagilsk in the Urals, Congonhas do Campo in Brazil, Rezbanya, Moldawa, and Tarnowitz. Used as a pigment, but not permanent.

356. Pn<ENico-CHRθiTE,2i ’ bCr + Pb. Right prismatic; dimensions unknown. H. =3 to 3 ’ 5; G. =575. Translucent on the edges; resinous or adamantine. Cochineal-to hyacinth-red; streak brick-red. C.c.: 23 chromic acid, and 77 protoxide of lead. Berezoff.

357. Vauquelinite, 2(2tbCr + Lb) + (20uCr + 0u).

Oblique prismatic, C 67° 15'. Crystals OP, - P, - po 00 (or P f, Ä), always twinned (fig. 410), the faces of OP forming an angle of 134* 30'; also botryoidal or reniform. H. =2'5 to 3; G. =5'5 to 5'8. Semitranslucent or opaque; resinous. Blackish or dark olive-green; streak siskin-green. C.c.: 61 lead protoxide, 11 copper protoxide, 28 chromic acid. Leadhills, Berezoff, Congonhas do Campo (Brazil).

MOLYBDATES AND TUNGSTATES.

358. Wulfenite, f ’ bMo.

4 A⅛ d ⅛ p p 13 Γ∙i 8 ι' 0P ^> W),P, -P(m), ∞P2(r)(figs. 411-414). LI. r; brittle; fracture uneven, or conchoidal. H. =3; G. =6 ’ 3 to 6’9. Pellucid; resinous to adamantine. Orangeyellow, honey-yellow, and colourless. C.c.: protoxide of lead 61 - 5, ιnolybdic acid 38 - 5; red varieties have some chromic acid. Lacken tyre in Kirkcudbright (fig. 412), Bleiberg, Rezbanya, Pennsylvania, Zacatecas. 2PbOMoO 3 + CaOMoO 3 , with 6 - 88 of lime, occurs in Chili.

Pyramidal. OP (c): p' 117° 10'; p , : p 125° 40' (fig. 415). H. = 3 to 4. Colour deep aurora-red. Streak orangeyellow. A vanadio-molybdate of lead. Leadhills.

360. Megabasite, Mg 4 W 8 .

Oblique prismatic; similar to wolframite. In fine needles. H. =3'5 to 4; G. = 6 ’ 45 to 6 97. Vitreous to adamantine. Yellowish brown to brownish red, translucent hyacinth-red; streak ochre-yellow. C.c.: protoxide of manganese 231, protoxide of iron 5‘4, tungstic acid 71'5. Schlaggenwald, Sadis dorf, Morococha in Peru.

361. Scheelite, CaW.

Pyramidal; with many of the modifying planes hemihedric. P. 113° 32'. Cl. 2P∞ (n) 130° 33', perfect; P and OP less so. Fracture conchoidal. H. = 4 to 4 5 ; G. — 5 ’ 9 to 6 ’ 2. Translucent; resinous to adamantine. Colourless, and grey, yellow, or brown; streak white. C.c.: 19 ’ 4 lime, 80'6 tungstic acid. Caldbeckfell near Keswick, Pengelly in Cornwall, Zinnwald, Schlaggenwald, Salzburg, Chili, Siberia, Connecticut. Employed for the extraction of yellow tungstic acid, a fine pigment.

362. Stolzite, PbW.

Pyramidal, generally hemihedric. P. 131® 25'. Crystals sometimes spindle-shaped. Cl. P, imperfect. H. — 3; G. = 7'9 to 8 Ί. Translucent; resinous. Grey, vellow, brown. C.c.: 48 ’ 4 protoxide of lead, 51 ’ 6 tungstic acid. Keswick, Zinnwald, Coquimbo (Brazil).

363. Reinite, FeW .

Pyramidal. P 103° 32'; basal angle 122° 8'. Cl. ooP. H. = 4: G. =6 , 64. C.c.: protoxide of iron 23'4, tungstic acid 75'45. Kimbosan in Japan.

364. Wolframite, (Êe, Mn) W.

Oblique prismatic, C 89° 22'. α>P (Μ) 100° 37', -⅛P 0 α> <P' 1 61° 54', P c oo (u) 98° 6', ooP∞ (r), ooP 0 2 (5), - P (a), ⅛2P c 2(s). Twins common. Also laminar.

Cl. clinodiagonal, perfect; fracture uneven. H. =5 to 5'5; G.=7Ι to 7'5. Opaque; resinous, metallic, adamantine on the cleavage. Brownish black; streak black (varieties with most iron) to reddish brown (most manganese). C.c.: 76 tungstic acid, 9'5 to 20 protoxide of iron, and 4 to 15 protoxide of manganese, in some with 1Ί niobic acid. East Pool, Carnbrae, and mines near Redruth; Godolphin’s Ball in Cumberland; Altenberg, Geyer, Ehrenfriedersdorf, Schlaggenwald, Zinnwald, the Harz; also Urals, Ceylon, and North America.

Ferberite, with 26 protoxide of iron and 2ËeW + Fe (H. =4 to 4'5; G. =67 to 6'8), from Spain, may be different.

365. Hübnerite, MnW.

Right prismatic. a>P(J∕). JZ:JZ105°. Cl. oofαo, perfect; usually foliated or columnar. H. = 4 '5; G. = 7 '14. Adamantine on cleavage;* elsewhere greasy. Brown-red; streak yellow-brown. C.c.: protoxide of manganese 23'4, tungstic acid 76'6. Mammoth district in Nevada.

ANHYDROUS PHOSPHATES, ARSENIATES, AND VANADIATES.

366. Xenotime, Y 8 ⅛.

Pyramidal. P 82° 22' middle angle; polar angle 124° 30’. Crystals P; α>P; α>Poo. Cl. ooP.

H. =4'5; G. =4 ’ 6 to 4'55. Translucent in thin splinters; resinous. Yellowish and flesh-red. C.c.: 62 yttria, and 38 phosphoric acid; but some with 8 to 11 cerium protoxide. Lindesnaes and Hitterö in Norway, Ytterby (Sweden), Georgia, and (Wiserine} St Gotthard,

367. Cryptolite, Ce 8 P 2 .

Acicular crystals, embedded in apatite.

G. = 4'6. Transparent. Pale wine-yellow. Powder sol. in con. s. acid. Wöhler found 7370 cerium protoxide, 27 '37 phosphoric acid, and 1'51 iron protoxide. Occurs in the apatites of granite in Scotland, but not in those of limestones. Also at Areudal.

368. Monazite, (Ce, La, Th) 3 P 2 .

Oblique prismatic, C 76° 14 ’. ooP 93° 23'; crystals (fig. 420) generally thick or tabular. Cl. basal, perfect; translucent on edges. Flesh-red and reddish brown. C. c.: 28 phosphoric acid, 37 to 46 cerium protoxide, 24 to 27 lanthanum oxide; that from Zlatoust from 18 to 32'5 of thoria. Nöterö in Norway, Miask, Norwich in Connecticut, and the Rio Chico in Colombia. Turncrite, from Dauphiné, in comple^transparent honey-yellow crystals, is monazite.

369. Triphylite, (2Fe + Li a )F 2 .

Right prismatic. 00P 133°; chiefly granular. H. =5; G. ∙=3 , 6. Resinous. Greenish grey with blue spots. C.c.: iron protoxide 40, manganese protoxide 5’5, lithia 7 '5, phosphoric acid 45. Bodenmais in Bavaria, Norwich in Massachusetts. Lithiophilite, from Fairfield (Connecticut), is a manganesian triphylite.

370. Berzeliite {Kuhnite), (CaMg) 3 λ's 2 .

Massive. H.—5 to 6; G. =-2 - 52. C.c.: lime 23, magnesia 15, arsenic acid 60. Sol. in n. acid. Lângban (Sweden).

371. Arseniate of Nickel, Ni 3 As 2 .

Amorphous. H. =4; G. = 4'98. Sulphur-yellow. C.c.: oxide of nickel 48’2, arsenic acid 50’5. Johann-Georgenstadt.

372. Nickelerz, Ni 3 As a + 2Ni.

Crystalline massive. G. =≈4 - 84. Dark grass-green; streak lighter. C.c.: oxide of nickel 62Ί, arsenic acid 36’6. Johann-Georgenstadt.

373. Dechenite, (PbZn)V 2 .

Botryoidal and stalactitic. H. =3 to 4; G =5’82. Lustre resinous to greasy. Yellowish red, deep red; streak orange to pale yellow. C.c.: 57’7 oxide of lead, 15'8 oxide of zinc, 24’2 of vanadic acid. Wanlockhead, Freiburg (in Baden), Lauter Valley.

374. Psittacinite, 3(Pb 3 V 2 )+ Cu 3 V 2 +6Cιιli a .

Mammillated and incrusting. Siskin-to olive-green. C.c.: vanadic acid 19’3, lead oxide 53’2, copper oxide 18’95, water 8’58. Silver Star (Montana).

375. Pucherite, Bi 2 V a .

Right prismatic. ∞P 123° 55'. H. = 4; G. = 6’25. Cl. basal, perfect; vitreous. Red or reddish brown; streak yellow. Easily soluble in acids. C.c.: bismuth oxide 71 ’7, vanadic acid 28 ’3. Schneeberg.

376. Atopite, Ca 2 S'b 2 .

Cubic (figs. 30 with 26 and 33). H. ≡5 ’ 5 to 6; G. = 5. Lustre greasy; yellow to resin-brown. Translucent. C.c.: antimonic acid 73’2, lime 17’5, iron protoxide 2’7, magnesia 1’5, soda 4’3. Lângban (Wermland).

HYDROUS PHOSPHATES, &c.

377. Brushite, (⅜Ca + ⅜H a ) 3 P 2 + 4H 2 .

Oblique prismatic, C 62° 45'. Needle crystals. H. =2 to 2’5; G. =2’21. Vitreous. C.c.: lime 32’6, phosphoric acid 41’3, water 26 '4. Aves Islands and Sombrero (Antilles).

378. Newberyite, Mg a H 2 , 'i i 2 + 6H 2 .

Right prismatic. Cl. brachydiagonal. C.c.: phosphoricacid 41’25, magnesia 23, water 35’7. From guano, Skipton Caves, Victoria.

379. Haidingerite. Ca 2 As a + 30 2 .

Right prismatic. ∞P 100°. Cl. perfect; sectile, flexible. H. =2 to 2’5; G. =2’8 to 2’9. Otherwise like pharmacolite (sp. 381). C.c.: 85’68 arseniate of lime, and 14’32 water. Joachimsthal.

380. Roselite, É 3 À’s 2 + 2H 2 .

Anorthic. Cl. macrodiagonal. Rose-red; streak white. H. = 3’5; G. =3’46. C.c.: 25 5 lime, 10’3 cobalt oxide, 3’6 magnesia, 52 ’4 arsenic acid, 8 ’2 water. Schneeberg.

381. Pharmacolite, 2CaAs 2 + 6H 2 .

Oblique prismatic, C 65’ 4' (fig. 421). α>P (∕) 117° 24', -P (Z) 139’ 17', - ⅛P (n) 141’ 8', ⅜P 0 ∞ (o) 83° 14', ooP°3 {g) 157 β 5'. Crystals generally acicular and radiated. Cl. clinodiagonal, perfect; sectile, and flexible. H. =2 to 2’5; G. =2’6 to 2’8. Translucent; vitreous. Pearly white. Yields water in the closed tube. C.c.: arsenic acid 51, lime 25, water 24. Andreasberg, Bieber, Mar-kirchen, Wittichen. Generally mixed with erythrite or annabergite.

382. Wapplerite, 2CaAs + 8H 2 .

Anorthic; ooP' (m), α>T (Jf ), oop'2 (n), ooT.2 (A 7 ), ,P'a> (<Z), 'P,oo (D), 3,t>'oo (i), 3'P,oo (T), 2P'2(p), 3P'⅜(s-), 3'P⅜ (G i ), 4,P4 (ω), 2,P2 (<r), ooP∞ (&) (fig. 422); also incrusting and globular. Cl. clinodiagonal. H. = 2 to 2 - 5; G. = 2’48. Colourless. Vitreous. C.c.: lime 15’6, magnesia 7’4, arsenic acid 17'5, water 29’5. Joachimsthal.

383. Hörnesite, Mg 3 A's 2 + 8H 2 .

Oblique prismatic. α>P 107°. H.

-=5 to 1; G. —2’47. White. Translucent; pearly. C.c.: 24’3 magnesia, 2914 water, 46 ’56 arsenic acid. Probably from Hungary.

384. Vivianite, 3FeP 2 + 8H 2 .

Oblique prismatic, C 75° 34 ’. ooP {m) 108 β 2'; P (t>) 120’ 26', P o ∞ (w) 54° 40'. Crystals prismatic (figs. 423, 424); also fibrous or earthy. Cl. clinodiagonal, perfect; thin laminae flexible. H. =2; G. =2’6 to 2’7. Translucent or transparent; vitreous, or bright pearly on cleavage. Indigoblue to blackish green; streak bluish white, but soon becomes blue on exposure. C.c.: 33’1 iron protoxide, 12’2 iron peroxide, 29 phosphoric acid, and 25’7 water. Transparent indigocoloured crystals at St Agnes in Cornwall, and Allentown and Imleytown in New Jersey; earthy in Cornwall, Styria, North America, Greenland, and New Zealand; and in peat mosses in northern Germany, Sweden, Norway, and Shetland.

385. Symplesite, Fe 3 As 2 + 8H a .

Oblique prismatic; in minute acicular crystals. Cl. clinodiagonal. H. = 2’5; G. =2’96. Vitreous. Cleavage face pearly. Celadon-green to pale indigo; streak bluish white. Lobenstein in Reuss, and Lölling in Carinthia.

386. Erythrite, Co 3 Xs 2 + 8H 2 .

Oblique prismatic, C 55° 9'. ooP c ∞ (P), α>P 0 oo {T), Poo (Μ); also ooP3 (⅛), and P (Z) 118° 23' (fig. 425). Cl. clinodiagonal (P), perfect; sectile; thin laminae flexible. H. = 1’5 to 2’5; G. = 2’9 to 3. Translucent; vitreous, pearly on the cleavage. Crimson or peachblossom-red. C.c.: 38’2 arsenic acid, 37’8 cobalt protoxide, 24 water, but often with nickel 9. Cornwall, Alston in Cumberland, Alva in Stirlingshire, Schneeberg, Saalfeld, Allemont, Riechelsdorf, the Pyrenees, and Modum in Norway. Kobaltbeschlag or Earthy Incrusting Cobalt, reniform, is a mixture of erythrine with arsenious acid. Lavendulan, thin reniform lavenderblue crusts, translucent, resinous, or vitreous (H. =2’5 to 3; G. = 2’95 to 3 1), consisting of arsenic acid, protoxides of cobalt, nickel, and copper, with water; from Annaberg.

387. Köttigite, (Zn, Co, Ni) 3 As 2 4- 8H 2 .

Oblique prismatic; massive or in crusts, with crystalline surface and fibrous structure. Cl. clinodiagonal, perfect. H. = 2 ’5 to 3; G. = 31. Lustre of fracture silky. Colour light carmine and peachblossom-red, of different shades; streak reddish white. Translucent to subtranslucent. C.c.: 30’52 zinc oxide, 6’91 cobalt oxide, 2 nickel oxide, with arsenic acid. Schneeberg.

388. Annabergite {Nickel Ochre), 3⅛ι 3 As + 8⅛ 2 .

Oblique prismatic; in capillary crystals, also earthy; sectile. H. =2 to 2’5; G =3 to 3’1. Dull or glistening. Apple-green or greenish white; streak greenish white and shining. C.c.: 38’7 arsenic acid, 37 ’3 nickel protoxide, and 24 water, but with a little cobalt or iron. Leadhills, Pibble in Kirkcudbright, Andreasberg, Saalfeld, Riechelsdorf.

389. Ludlamite, Fe 7 2P a + 9H 2 .

Oblique prismatic, C 79’ 27'. ∞P 131° 23'; 0P; P 111* 29' (fig. 426). Cl. 0P, perfect. H. =3’5; G.=312. C.c.:

53’05 oxide of iron, 29’88 phosphoric acid, 17 Ό water. Cornwall.

390. Fillowite, 3(R 3 P 2 ) + H 2 .

Oblique prismatic, C 89’ 51'; pseudo-rhombohedral. P; - 2Pδ; 0P. Cl. basal. H. =4’5; G. = 3’43. Resinous to greasy. Wax-yellow to red-brown, or colourless; streak white; translucent. C.c.: phosphoric acid 40∙2, iron protoxide 6’8, manganese protoxide 40’2, lime 5’2, soda 5’8, water 1 ’ 7. Branchville (Connecticut).

391. Hureaulite, 5(Mn, Fe)2'P a + 5H 2 .

Oblique prismatic, C 89° 27'. α>P 61°. Fracture conchoidal. H. =3’5; G. =3’2. Translucent; resinous. Reddish yellow or brown. B.B. fuses easily to a black metallic globule. Soluble in acids. C.c.: 39 phosphoric acid, 8 iron protoxide, 42 manganese protoxide, and 12 water. Hureaux near Limoges.

Heterozite. H.— 5; G.—3'5. Opaque; vitreous or resinous. Dark violet or blue to greenish grey; streak violet-blue or crimson-red. Contains more iron and less manganese than the above. Bureaux.

,, w

392. Dickinsonite, 4(R 3 Y , s ) + 3H 2 .

Oblique prismatic, C 60 β 30'. Crystals tabular. Cl. basal, perfect. H. —3 - 5 to 4; G. =3 , 34. Vitreous; pearly on cleavage. Oliveto oil-green, and grass-green; streak wnite. Transparent; brittle. C.c.: phosphoric acid 40, iron protoxide 127, manganese protoxide 25, lime 11 ’ 8, soda 6 - 6, water 3’8. Branchville (Connecticut).

393. Triploidite, (Mn, ie)jF 9 + 0 3 (itn, i ’ e) 2 .

Oblique prismatic, C 51’ 56'. Generally fibrous; transparent; resinous to adamantine. H. =4'5 to 5; G. = 37. Yellowish-brown. C.c.: 48'45 oxide of manganese, 14'88 protoxide of iron, 32 Ί phosphoric acid, 4Ί water. Fairfield (Connecticut).

394. Fairfieldite, fe 3 P 2 + 2⅛ 2 .

Anorthic; usually foliaceous. H. = 3'5; G. =3 - 15. White to straw-yellow; streak white. Pearly to brilliant-adamantine on cleavage. Transparent; brittle. C.c: phosphoric acid 38'4, iron protoxide 5'6, manganese protoxide 15'6, lime 30, soda 7, water 10. Fairfield (Connecticut).

395. Chondrarsenite, Mn 8 As 2 + ⅝H 2 .

In small grains. H. — 3. Yellow to reddish-yellow. Translucent; brittle; fracture conchoidal. Paisberg mines (Wermland).

396. Reddingite, Mn 3 P 2 + 3H 2 .

Right prismatic. P; P2; 00Poo. H. =3 to 3*5; G. —31. Vitreous; rose-pink to yellowish white. Translucent; fracture uneven; brittle. C.c.: phosphoric acid 34'5, iron protoxide 5'43, manganese protoxide 46'3, lime - 8, water 13 ’ 1. Branchville.

397. Scorodite, Fe 2 As 2 + 4H 2 .

Right prismatic. P with polar edges 102’ 52' and 114° 40'. Crystals P (p), 00P00 (a), and oof 00 (5); also OP, ⅛P (i), 00P (n), 2P2 (s), ooP2 (d) 120" 10', and 2P∞ (τn) 132" (fig. 427); also columnar and fibrous. Cl. imperfect; brittle. H. — 3 ’ 5 to 4; G. =3 ’ 1 to 3*2. Translucent; vitreous. Leek-green to greenish black, also indigoblue, red, and brown. B. B. fuses easily, with arsenical odour, to a grey magnetic slag. Sol. in h. acid, to a brown solution. C.c.: 49 - 8 arsenic acid, 34 ’ 6 iron peroxide, and 15'6 water. St Austell in Cornwall, near Limoges in France, Schwarzenberg, Lölling in Carinthia, Brazil, and Siberia.

398. Strengite, Fe 2 P 2 +4H 2 .

Right prismatic. P with polar edges 101’ 38' and 115" 36', middle edge 111’ 30'. 00P2 (d) and 00Poo (r), P (P), 0P (A), 2P00 (m) 48° (fig. 428). Crystals generally r, P, d; r dominant. Cl. r. H. — 3 to 4; G. = 2'87. Cherry-red. Translucent. C.c.: protoxide of iron 43 ’ 18, phosphoric acid 37 ’ 42, water 19 ’ 4. Rock Bridge (Virginia).

399. Dufrenite (Kraurite), 2Fe 2 P 2 + 30 2 .

Right prismatic. 00P about 123". Spherical or reniform. Cl. brachydiagonal; brittle. H.-3 to 35; G.-3'3 to 34. Translucent on the edges, or opaque; shining or dull. Dirty leek-green or blackish green; streak siskin-green. C.c.: 63 iron peroxide, 28 phosphoric acid, and 9 water. Westerwald, Hirschberg, and Limoges.

400 Beraunite, 5B⅛ 2 3⅜* 2 +140 2 .

Occurs in small foliated and columnar aggregates. Cl. plane metallic pearly. H. — 2; G. — 2'878. Colour hyacinth-red to reddish brown; streak dirty-yellow. C.c.: 54 ‘5 peroxide of iron, 28 ’ 65 phosphoric acid, and 16 ’ 55 water. Bohemia, Scheibenberg in Saxony.

401. Eleonorite, 3Fe 2 2P 2 + 8⅛ 2 .

Oblique prismatic. C 48’ 33'. Twin face the orthopinacoid. Cl. 00P o co. H. =3 to 4. Dark hyacinth-red; streak yellow. Vitreous to pearly. C.c.: 51'94 peroxide of iron, 31 ’88 phosphoric acid, 16 , 37 water. Eleonore mine near Bieber.

402. Cacoxene, 2Fe 2 P 2 + 12H 2 .

Radiated tufts, of a brownish-yellow colour. H. = 3 to 4 ∙ G. =3∙38. Sol. in h. acid. From the Hrbeck mine near Zbirow in Bohemia.

403. Pharmacosiderite (Cube Ore), 4Fe 2 3As 2 + 15⅛ 2 .

Cubic and tetrahedral; usually 00O<≈0, with θ, or 00 O. Brittle.

H. =2’5; G. — 2 ’ 9 to 3. Cl. <×>O∞. Semitransparent to translucent; adamantine or resinous. Oliveto emerald-green, honeyyellow, and brown; streak straw-yellow. Pyro-electric. C.c.: 43 arsenic acid, 40 iron peroxide, and 17 water. Carharrack in Cornwall, Burdle Gill in Cumberland, Lobenstein in Reuss, Schwarzenberg in Saxony, North America, and the gold quartz of Australia.

404. Calaite (Turquoise), 2(A1 2 )P 2 + 5H 2 .

Massive, reniform, or stalactitic; fracture conchoidal. H. ≈ 6; G. = 2 '6 to 2'8. Opaque or translucent on the edges; dull or waxy. Sky-blue, greenish blue, rarely green; streak greenish white. C.c.: 47 alumina, 32'5 phosphoric acid, and 20 5 water, but mixed with phosphate of iron and copper. Silesia, Lusatia, and Reuss. Oriental turquoise, in veins, at Meshed, near Herat; in pebbles in Khorasan, Bokhara, and Syrian desert. Takes a fine polish, and is valued as an ornamental stone, but is destroyed by oil, and deteriorated by soap.

405. Wavellite (Lasionite), 3A1 2 2P 2 +12⅛ s .

Right prismatic. 00P 126" 25; Poo 106* 46'. Crystals 00P00 (P), 00P (d), Poo (0) (fig. 429); but generally small, acicular, and in radiated-hemispherical and. stellate-fibrous masses. Cl. along 00P and Poo, perfect. H. -3'5 to 4; G. =2 3 to 2'5. Translucent; vitreous. Colourless, but generally yellowish or greyish, sometimes green or blue. C.c.: 38 alumina, 35'3 phos-Shoric acid, and 26 7 water; but generally traces of uoric acid (2 per cent.). Shiant Islands and Glencoe in Scotland, Barnstaple, St Austell, near Clonmel and Portrush, Beraun in Bohemia, Amberg in Bavaria; also in New Hampshire and Tennessee. C<xruleolactin, from Nassau, has two equivalents less of water.

406. Variscite, A1 2 P 2 + 4H 2 .

Right prismatic; reniform; conchoidal fracture. H. = 4 to 5; G. = 2 , 34 to 2 ’ 38. Apple-and emerald-green; streak white. C.c.: 32 ’ 4 alumina, 44'85 phosphoric acid, 2274 water. Messbach in Reuss, Montgomery county in Arkansas.

Zepharovichite from Bohemia contains one equivalent more water; Evansite from Hungary two equivalents more.

407. Fischerite, 2A1 2 P 2 + 8⅛ 2 .

Right prismatic. α>P 118’ 32'; generally in crystalline crusts. H. =5; G. =2 ’ 46. Grass-and olive-green. Vitreous lustre. C.c.: alumina 42, phosphoric acid 29, water 29. Nijni-Tagilsk.

408. Peganite, 2A1 2 P 2 + 6H 2 .

Right prismatic. 00 P 127". In thin reniform crusts, of fibrous structure. H. =3 to 4; G. =2'49 to 2'54. Grass-and emeraldgreen. Vitreous or greasy lustre. C.c.: alumina 45, phosphoric acid 31'3, water 237. Striegis in Saxony.

409. Hopeite, Zn 3 P + 4H 2 .

Right prismatic. 00 P2 82’ 20'; P with polar edges 106’ 36' and 140". Cl. macrodiagonal, perfect. H. — 2 ’ 5to3; G. — 2 76 to 2 ’ 85. Vitreous or pearly. Greyish white. C.c.: oxide of zinc 35*21, phosphoric acid 31 '1, water 15'8. Altenberg.

410. Adamite, 4ZnAs 2 + II 2 .

Right prismatic. 00P 91’ 52'. Cl. macrodomic. H. =3'5; G. — 4 '34. Lustre vitreous. Colour honeyyellow to violet; streak white. Transparent. C.c.: oxide of zinc 56'6, arsenic acid 40'2, water 3'2. Cape Garonne in France, Cha&arcillo in Chili.

411. Libethenite 4CuP 2 + 6H 2 .

Right prismatic. <»P (u) 92’ 20', Ï’ ∞ (0) 109" 52', and P (fig. 430). H. =4; G. =3'6 to 3'8. Translucent on the edges; resinous. Leek-, olive-, or blackish-green; streak olive-green. C.c.: 66 copper protoxide, 30 phosphoric acid, and 4 water. Gunnislake (Devon), Libethen (Hungary), Nijni-Tagilsk.

412. Olivenite, 40u (As 2 P 2 ) + H 2 .

Right prismatic. oo(P) (r) 92° 30', Pα> (Z) 110° 50', 00P∞ (n) (fig. 431); also spherical and reniform, and columnar or fibrous. Cl. (r) and (Z), imperfect. H. = 3; G. = 4'1 to 4 '6. Pellucid in all degrees; vitreous, resinous, or silky.

Leek-, olive-, or blackish-green, also yellow or brown; streak olive-green or brown.

B. B. in the forceps fuses easily to a dark brown adamantine bead, covered with radiating crystals; on charcoal detonates, emits arsenical vapours, and is reduced. Sol. in acids and ammonia. C.c.: 56‘5 copper protoxide, 39 '5 arsenic acid, and 4 water; but also 1 to 6 phosphoric acid. Carharrack, Tin Croft, Gwennap, and St Day in Cornwall; Alston Moor, Thuringia, Tyrol, Siberia, Chili.

413. Veszelyite, 9Cu, 6Zn, P 2 , As 2 + 18H 2 .

Oblique prismatic, C 103° 50'. H. =3*5 to 4; G. =3’53. Greenish blue. C.c.: copper 37'34, 25'20 zinc oxide, 10'41 arsenic acid, 9Ό1 phosphoric acid, 17'05 water. Moravicza (Banat).

414. Descloizite, 2PbV 2 + ⅛ 2 .

Right prismatic. ∞P 116° 25'. H. =3'5; G. =5'86 to 6'1. Olive-brown to black. C.c.: 56'48 oxide of lead, 16'6 oxide of zinc, 1Ί6 oxide of manganese, 22'74 vanadic acid. Sierra de Cordoba in the Argentine Republic.

415. Volborthite, 4(Cu, Ca) V 2 + H 2 .

Hexagonal; small tabular crystals, 0P, ∞P, single or in groups. Generally massive. H. =3; G. =3'45 to 3'89. Olive-green; streak almost yellow. B.B. on charcoal fuses easily and forms a graphite-like slag, containing grains of copper. Sol. in n. acid, and with water gives a brick-red precipitate. C. c.: 37 to 38 vanadic acid, 39'4 to 46 copper oxide, 18'5 to 13 lime, 3'6 to 5 water. Sissersk (Urals), Nijni-Tagilsk, and Friedrichroda in Thuringia.

416. Tagilite, 4CuP 2 + 3H 2 .

Oblique prismatic; but botryoidal and radiating-fibrous, or earthy. H. =3; G. =4. Emerald-green. C.c.: 61'8 copper protoxide, 27'7 phosphoric acid, and 10'5 water. Nijni-Tagilsk, and near Hirschberg.

417. Euchroite, 40uAs 2 + 7¾.

Right prismatic. ooP (J∕) 117° 20', Poo(n) 80° 52', with ∞⅛2 (Z) and 0P (P) (fig. 432). Brittle. H.=3'5 to 4; G. = 3'35 to 3'45. Translucent; vitreous. Emerald-or leek-green; streak verdigris-green. B.B. in forceps fuses to a greenish brown crystallized mass. Easily sol. in n. acid. C.c.: 47 copper protoxide, 34 arsenic acid, and 19 water. Libethen in Hungary.

418. Erinite, 5CuXs 2 + 2H 2 .

Reniform and foliated; conchoidal fracture. H. = 4'5 to 5; G. =4 to 4 1. Translucent on the edges; dull resinous. Emerald-or grass-green; streak similar. C.c.: 59'9 copper protoxide, 34'7 arsenic acid, and 5'4 water. Cornwall. Cornwallite has 3 or 5 of water.

419. Dihyrite, 5CuP 2 + 2⅛ 2 .

G. = 4 ’ 4. Oxide of copper 69, phosphoric acid 24'7, water 6'25. Rheinbreitenbach and Nijni-Tagilsk.

420. Mottramite, 5(0u, Pb)V' 2 + 2H 2 .

Black crystalline crusts; streak yellow. H. = 3; G. = 5 '9. C.c.: oxide of copper 20'4, oxide of lead 7'2, vanadic acid 18'7, water 3'7. Mottram in Cheshire.

421. Ehlite 5CuF 2 + 3H 2 .

Right prismatic; botryoidal, radiating, foliated. H. = 1 '5 to 2; G. = 3 '8 to 4 '27. Translucent on the edges; pearly on the cleavage. Verdigris-green; streak paler. C.c.: 67 copper protoxide, 24 phosphoric acid, and 9 water. Ehl on the Rhine, Nijni-Tagilsk, Libethen.

422. Tyrolite, 5CuAs 2 + 9H 2 .

Right prismatic. Cl. basal, perfect; reniform. Radiate-foliaceous. H. =1'5 to 2; G. =3. Lustre pearly on cleavage face. Colour apple-green and verdigris-green to sky-blue; streak paler. Subtranslucent. C.c.: oxide of copper 50'3, arsenic acid 29'2, water 20'5. Tyrol, Hesse, Thuringia.

423. Phosphorochalcite (Lunnite), 6CuP 2 + 3H 2 .

Oblique prismatic. Crystals ∞P c 2 (∕) 38° 56', P (P) 117° 49', with 0P (a) and α>P 0 ∞ (e) (fig. 433); usually small and indistinct; more common in spherical or reniform and radiated-fibrous masses. H. = 5; G. = 4 Ί to 4'3. Translucent throughout or on the edges; adamantine to resinous. Blackish-, emerald-, or verdigris-green. C.c.: 70'8 copper protoxide, 21'2 phosphoric acid, and 8 water. Cornwall, Rheinbreitenbach, Nijni-Tagilsk.

424. Clinoclase, 6CuAs 2 + 3H 2 .

Oblique prismatic, C 80° 30'. 0P (P), ∞P(ffl) 56°, ⅜P°oo (a) 99° 30', (r) 123° 48' (figs. 434, 435); and hemispherical. Cl. basal, perfect. H. = 2 , 5 to 3; G. = 4 '2 to 4 '4. Translucent; vitreous; pearly on cl. Dark verdigris-green to sky-blue; streak blue. C.c.: 62'6 copper protoxide, 30'3 arsenic acid, 7 '1 water. Cornwall, Tavistock, Erzgebirge.

425. Mixite.

Oblique prismatic or anorthic (?). Radiating, centrally granular. ooP 125°. H. =3 to 4; G. =2'66. Emerald-green to blue-green; streak paler. C. c.: 43 '21 copper oxide, 13'1 bismuth oxide, 30'45 arsenic acid, 11'1 water. Geistergang, Joaehimsthal.

426. Rhagite, 5Bi 2 2As 2 +8H 2 ·

Grape-like groups of minute crystals. Colour yellowish green; streak white. Lustre wax-like; brittle. H. = 5; G. = 6 '82. C. c.: bismuth oxide 79'5, arsenic acid 15'6, water 4'9. Neustädtel near Schneeberg.

427. Trögerite, 3UAs 2 + 12H 2 .

Oblique prismatic, C 80°. Crystals thin tabular. Cl. clinodiagonal, perfect. Lustre pearly. G. =3'3. Lemon-yellow. C.c.: 65'95 oxide of uranium, 17'56 arsenic acid, 16 '49 water. In closed tube gives off water, and becomes golden brown, but again yellow on cooling. Neustädtel.

428. Struvite, (NH 4 , 2Mg) P 2 + 12H 2 .

Right prismatic. Poo (a) 63° 7', f∞ (c) 95°, 4? ∞ (δ) 30° 32', ooPoo (n), ⅜P∞ (to) 123 o , 0P (o) (fig.

436). Cl. brachydiagonal, perfect. H. = 1 '5 to 2; G. = 1 '66 to 1 '75. Transparent or opaque; vitreous. Colourless, but yellow or brown. C.c.: 29'9 phosphoric acid, 16'3 magnesia, 10'6 ammonia, and 44 water. Under St Nicholas church at Hamburg, and in guano from South America.

429. Arseniosiderite, 3CaAs 2 + 3Fe 2 As 2 + 6H 2

Spherical and fibrous; friable. H. =1'2; G. =3'52 to 3'88. Opaque; silky. Golden yellowish brown; streak yellowish brown. C.c.: peroxide of iron 39'4, lime 13'8, arsenic acid 37'9, water 8'9. Romanèche near Macon.

430. Chalcosiderite.

Anorthic. Light green crystals. G. =3'11. C.c.: 42'8 peroxide of iron, 8'1 oxide of copper, 4'45 alumina, 30'54 phosphoric acid, 15 water. Cornwall.

431. Lazulite, A1 2 P 2

+ (Mg, Fe) 3 P 2 + 2H 2 .

Oblique prismatic, C 88° 2'. ooP 91° 30', P (e) 99° 40', - P (p) 100° 20'. Crystals often tabular through distortion; twins on 0P, and ooP 0 coj also massive; fracture splintery. Cl. oo P. H. = 5 to 6; G. =3 to 3*1. Translucent; vitreous. Indigo-and smalt-blue to greenish; streak white. In closed tube yields water, and loses colour. Soluble in acids after ignition. C.c.: 31'7 alumina, 10 magnesia, 6 protoxide of iron, 44 phosphoric acid, and 6 water. Salzburg, Styria, Brazil, Georgia, Lincoln in North Carolina.

432. Childrenite, 2(Èe, Mn)JP'+AlP'+15H. P-P 2 ,H = H 2 ,Ac.

Right prismatic. Polar edges 101° 43', 130° 1O', middle 98° 44'; usual form P, 2É», ooP∞ (e, oe, P, fig. 439). H.-4’5 to 5; G.=3 - 18 to 3’3. Translucent; vitreous. Yellowish white to wine-or ochre-yellow. brown, Or almost black. C.c.: 307 iron protoxide, 9 manganese protoxide, 14’5 alumina, 29 phosphoric acid, and 17 water. Tavistock, Crinnis and Callington (Cornwall).

433. Eosphorite (Fe, ⅛i) 2 A1, P i +40.

Right prismatic. P (p) 133° 32' and 118° 56'; α>P (ιj 104° 19'; ∞Pα> (a), oof oo (⅛), oof 2 (g), ⅜P⅜ ⅛), 2f 2 (s) (polar edges 130° 26' and 98° 42') (fig. 440). Cl. macrodiagonal. H. — 5; G. — 3Ί3. Pale red. Vitreous. C.c.: 22 alumina, 7’4 protoxide of iron, 23’5 oxide of manganese, 31 '5 phosphoric acid, 15’6 water. Fairfield (Connecticut).

434. Liroconite, Cu 8 ⅛s + AlAs + 24H.

Oblique prismatic, C 88° 33'. ooP (d) 61° 31', P e oo (o) 74° 21' (fig. 349). H. =2 to 2’5; G. =2’8 to 3. Translucent; vitreous or resinous. Azureblue to verdigris-green; streak paler. C.c.: 36 ’ 6 protoxide of copper, 1Γ9 alumina, 26’6 arsenic acid, 24’9 water. Redruth, Herrengrund in Hungary.

435. Chalcophyllite, 0u 6 As +12H.

Hexagonal rhombohedral; R 69° 48' (fig. 441). Cl. basal, perfect; sectile. H.-2; G. =2’4 to 2 ’ 6.

Transparent; vitreous to adamantine. Pearly on OR (o). Emerald-to grass-and verdigris-green; streak pale green. Soluble in acids and ammonia. C.c.: protoxide of copper 49’6, arsenic acid 18, water 32 - 4. Redruth in Cornwall, Saiαa in Saxony, Moldawa in the Banat.

436. Uranite, (0a, U 2 ) P + 8H.

Right prismatic. »P 90’ 43'; P middle edge 127° 32'. 0P: P 116-14; 0P: 2Pα> 109° 6'; 0P: 2f co 109° 19' (figs. 442, 443). Crystals flat. CL basal, perfect; sectile. H. =1 to 2; G. =3 to 3 ’ 2. Translucent; pearly on 0P. Sulphur-yellow to siskin-green; streak yellow. C.c.: 15’5 phosphoric acid, 62’6 uranium peroxide, 6 - l lime, and 15’8 water.

Cornwall, Autun and Limoges in France, Johann-Georgenstadt and Eibenstock in Saxony, Chesterfield in Massachusetts.

437. Uranospinite, (Ca, ⅛F 2 )⅛s + 80.

Right prismatic; quadrangular, scale-like crystals. Cl. basal, perfect. H. =2’3; G. =>3’45. Siskin-green. C.c.: lime 5’47, sesquioxide of uranium 59 , 18, arsenic acid 19 - 37, water 16’29. Neustädtel.

438. Uranocircite, (Èa, U 2 )⅛ + 8H.

Yellowish green crystals, isomorphous with 437. Cl. basal. G. =3 , 53. C.c.: sesquioxide of uranium 56’86, baryta 14’57, phosphoric acid 15’1, water 14. Falkenstein in Voigtland.

439. Chalcolite, (Cu, U 2 ) P + 8≡≡.

Pyramidal. P middle edge 142° 8'; P∞ 128° 14'. Crystals 0P, P, ooP<z>, P∞. Cl. basal, perfect; pearly lustre; brittle. H. =2 to 2’5; G. =3’5 to 3 ’6. Grass-to emerald-or verdigrisgreen; streak apple-green. C.c.: 15 , 2 phosphoric acid, 61 uranium peroxide, 8’5 copper protoxide, and 15’3 water. Redruth and St Austell, Johann-Georgenstadt, Eibenstock, Schneeberg Bodenmais, Baltimore.

440. Zeunerite, (0u'U 2 )⅛s + 8H.

Pyramidal. P middle edge 142° 6'. 0P: P 109° 57'. Crystals tabular. Cl. basal. H. =2’5; G. =3’53. Grass-green. Lustre pearly. C.c.: 7’7 oxide of copper, 55’95 sesquioxide of uranium, 14 water. Huel Gorland in Cornwall, Neustädtel, Joachimsthal, Zinnwald, Wittichen.

441. Walpurgite, 5BiAs + 3U⅛s + 100.

Anorthic; in scaly crystals. Wax-yellow to pomegranate-red. Adamantine to greasy. H. -3’5; G. = 576. C. c.: sesquioxide of bismuth 60’4, sesquioxide of uranium 20’4, arsenic acid 13, water 4’5. Neustädtel.

442. Plombgomme, fb 3 P + 6AlH 3 .

Reniform or stalactitic; fracture conchoidal and splintery. H. -= 4 to 4’5; G. —6’3 to 6’4. Translucent; resinous. Yellowish or greenish white to reddish brown. C.c.: 38 protoxide of lead, 35 alumina, 8 phosphoric acid, and 19 water; but with 2 chloride of lead. Poullauouen, Nuissière (near Beaujeu), Georgia.

Compounds of Phosphates, Vanadiates, and Arseniates with Haloid Salts.

443. Apatite, 30a⅛+Ca(Cl, F).

Hexagonal and pyramidal-hemihedric. P 80° 26'. The most common forms are ∞P (Μ); ooP2(n); 0P(m); P(ae); the base 0P seldom wanting (figs. 92, 95, 96, 97, 98). The crystals are short-prismatic or thick-tabular; also granular, fibrous, or compact; fracture conchoidal or splintery; brittle. H. = 5; G. =3’1 to 3’25. Transparent to opaque; vitreous to resinous. Colourless and white, but generally light green, grey, blue, violet, or red. C.c.: phosphate of lime (89 to 92’3), with chloride (to 11) or fluoride (to 7’7) of calcium, or both. Disseminated in granite, gneiss, mica and hornblende slates, primary limestones, and trap rocks; also in beds and veins. Sutherland, Ross, and Aberdeen, in granite and limestone; Cumberland, Devonshire, and Cornwall; in tin-mines in Saxony; Bohemia, St Gotthard, Tyrol; Kragerö in Norway, New York, Canada.

444. Pyromorphite, 3fb∙ 1 P + PbCl.

Hexagonal; P 80° 44'. Crystals α>P, 0P, with ∞P2, or P (Μ, P, x t fig. 444), occasionally thicker in the middle, or spindle-shaped; also reniform or botryoidal; fracture conchoidal or uneven. H. =3’5 to 4; G. =6’9 to 7. Translucent; resinous or vitreous. Colourless, but generally grass-, pistachio-, olive-, or siskin-green, and clove-or hair-brown, and scarlet (Leadhills). C.c.: 897 phosphate and 10’3 chloride of lead, but with 0 to 9 arseniate of lead, 0 to 11 phosphate of lime, and 0 to 1 fluoride of calcium. Elgin, Wanlockhead, also Cornwall, Derbyshire, Yorkshire, Durham, Cumberland, Wicklow;

Przibram, Mies, and Bleistadt in Bohemia; Berezoff, Phoenixville in Pennsylvania, and Mexico.

445. Vanadinite, 3Pb 3 V+PbCl.

Hexagonal; P 78° 46'. Forms α>P, 0P (o), P (2 ), 2P, ⅜P(∂⅜), ooP2, ooP⅜, 2P2 (fig. 445). Transparent to opaque; resinous. Honey-yellow to greyish brown; streak white. H. =3;

G. =6’8 to 7’2. C.c.: oxide of lead 70’83, vanadic acid 19 ’35, lead 7’2, chlorine 2’62. Wanlockhead, Windischkappel in Carinthia, Haldenwirthshaus in the Black Forest, Bolet in West-Gotland, Berezovsk, Zimapan in Mexico, Cordoba in the Argentine Republic.

446. Mimetesite, 3Pb 3 As + PbCl.

Hexagonal; P 81° 48'. Crystals ooP, 0P, P (figs. 91, 444), or P, OP. Cl. P; fracture conchoidal or uneven. H.=3∙5 to 4; G.=719 to 7’25. Translucent. Colourless, but usually honey-or wax-yellow, yellowish green or grey. C.c.: 907 arseniate and 9’3 chloride of lead; but part of the arsenic occasionally replaced by phosphoric acid. Leadhills, Huel Alfred and Huel Unity in Cornwall, Roughten Gill and Dry Gill in Cumberland, Beeralston in Devonshire, Johann-Georgenstadt, Zinnwald, Badenweiler, St Prix in France, Nertchinsk, and Zacatecas in Mexico.

447. Wagnerite, Mg 3 P + MgF.

Oblique prismatic, C 63° 25'. ooP 57° 35'. Cl. prismatic, and orthodiagonal imperfect; fracture conchoidal or splintery. H. — 5 to 5’5; G. =3 to 3’2. Translucent or transparent; resinous. Wineyellow and white. C.c.: 43’3 phosphoric acid, 11’4 fluorine, 37’6 magnesia, and 7 7 magnesium; but with 3 to 4 ’5 iron protoxide and 1 to 4 lime. Werfen in Salzburg.

448. Triplite, (Fe, Mn) s P + RF.

Oblique prismatic; only granular. Cl. · in two directions at right angles; fracture conchoidal. H. ≈=5 to 5’5; G. =3’6 to 3’8. Translucent or opaque; resinous. Chestnut-or blackish-brown; streak yellowish grey. C.c.: iron and manganese protoxides, with 33 phosphoric acid, and 7 or 8 fluorine. Limoges, ScWaggenwald.

449. Zwieselite, (f 1 e, h⅛n) 3 ^'+FeF.

Right prismatic; but only massive. Cl. basal, perfect. H. =4’5 to 5; G. =3’95 to 4. Brown; streak yellow. C.c.: like triplite. Zwiesel in Bavaria.

450. Amblygonite, 'A1 5 ⅛ j + (Li, Na) 5 P 3 + AlF 3 + (Li, Na)F.

Anorthic; crystals rare; coarse granular. Cl. OP, pearly, meeting two others at 105“ and 87* 40 ’. Fracture uneven and splintery. H. =6; G. =3 to 31. Translucent; vitreous. Greyish or greenish white to pale mountain-green. C.c.: 47'9 phosphoric acid, 34 '5 alumina, 6 9 lithia, 6 soda, and 8’3 fluorine. Penig, Arendal, Montβbras (Creuse, France), also Hebron and Paris in Maine. Montebrasite has no soda.

451. Durangite, (R 2 ) ⅛s + 2NaF.

Oblique prismatic; crystals like keilhauite (sp. 669). ooP 110 β 10'; P 112’10'. Cl. prismatic. H. = 5; G. =3’95 to 4. Bright orange-red; streak cream-yellow. Vitreous. C.c.: alumina 17’2, iron protoxide 9 ’ 2, arsenic acid 53, soda 13’1, fluorine 7’7. Durango (Mexico).

452. Herderite.

Right prismatic. P polar edges 77’ 20' and 141’ 16'; ooP 115’ 53'. Fracture conchoidal. H. =5; G. =2 9 to 3. Translucent; vitreous, inclining to resinous. Yellowish or greenish white. Ehrenfriedersdorf in Saxony. An anhydrous phosphate of alumina with lime and fluorine.

Phosphates with Sulphates and Borates.

453. Svanbergite.

Rhombohedral; R 90’ 35'. H. — 4’5; G. =2’57. Vitreous to adamantine. Honey-yellow, reddish brown, and rose-red; streak reddish. Subtransparent. C.c.: 37’8 alumina, 6 lime, 17’3 sulphuric acid, 12’8 soda, 17’8 phosphoric acid, 6‘8 water. Horr-sjöberg in Wermland.

454. Diadochite, Fe 3 F 2 + 2FeS 2 + 32H.

Reniform and stalactitic; fracture conchoidal. H. =3; G. = 1'9 to 2. Resinous; vitreous. Yellow or yellowish brown; streak white. C.c.: 36’7 iron protoxide, 14’8 phosphoric acid, 15’2 sulphuric acid, ’and 30’3 water. Gräfenthal and Saalfeld.

455. Pitticite, Fe 2 S 3 + 2Fe⅛s4-24H.

Reniform and stalactitic; brittle; fracture conchoidal. H. =2’3; G. =2’3 to 2’5. Translucent throughout, or on the edges; resinous to vitreous. Yellowish, reddish, or blackish brown, sometimes in spots or stripes; streak light yellow or white. C.c.: 35 iron peroxide, 26 arsenic acid, 14 sulphuric acid, and 24 water. In many old mines, as Freiberg and Schneeberg.

456. Beudantite.

Rhombohedral; R 91’18'. H. —3’5; G. =4. Vitreous. Olivegreen; streak greenish yellow. C.c.: oxide of iron 40’69, oxide of lead 24’05, sulphuric acid 13’76, phosphoric acid 8’97, water 9’77. Dernbach in Nassau, Cork in Ireland.

457. Lüneburgite (2Mg, - H) P + Mgβ + 7H.

Concretions of fibrous structure. C.c.: 25’2 magnesia, 29’83 phosphoric acid, 14’74 boracic acid, 30’23 water. Lüneburg.

ARSENITES.

458. Ecdemite, 1⅛ 5 As 2 + 2PbCl 3 .

Pyramidal. Cl. 0P. H·-2’5 to 3; G.=7Ι4. Pale green. Vitreous on cleavage; resinous on fracture. C. c.: oxide of lead 59 ’67, lead 22’2, arsenious acid 10’59,chlorine 7’58. Lingban in Wermland.

459. Trippkeite, CuAs.

Pyramidal; P 111’56'. Blue-green. Lustrous. Copiapo in Chili.

SILICATES.

Andalusite Group.

460. Andalusite, À’iSi.

Right prismatic. ∞P (m) 90’ 50', P<o (r) 109’ 4', Poo (s) 109° 51'.

Also columnar. Cl. m; fracture splintery. H. -7 to 7’5; G. =3’1 to 3 ’2. Pellucid; vitreous. Grey, green, red, or blue. B. B. infusible.

Not affected by acids. C.c.: alumina 63Ί, silica 36’9. Clashnaree (figs. 446 to 449) and Clovain Aberdeenshire, Marnoch and Botriphnie in Banffshire, Killiney Bay in Wicklow, Andalusia, Tyrol, Penig, Massachusetts, Litchfield in Connecticut.

Chiastolite. H. =5 to 5’5; G. =3. Pale grey, yellow, green, and red. A compound structure, formed of four double wedge-shaped crystals, arranged in contact with the angles of a square conoidal crystal placed in their centre, and imbedded in a paste of clay slate. The section of the compound structure forms a tesselated cross, the appearance of which varies with the portion of the crystal which is cut. Portsoy (fig. 450) and Boharm in Banffshire, Wicklow, Keswick and Skiddaw, Brittany, Pyrenees, Maine, New Hampshire, Nova Scotia, Canada.

461. Cyanite {Disthene , ), AÏSÏ.

Anorthic; generally broad-prismatic lengthened crystals, formed by two faces (m l t). m: t 106’ 15'; m: i 145’ 41'; p: m 93’ 15' (fig. 451). Hemitropes common, united by m. Also radiated. Cl. m, perfect; brittle.

H. =7, on cl. planes 5; G. =3’5 to 3’7. Pellucid; vitreous. Cl. pearly. Colourless, and red, yellow, green, grey, and blue. B.B. infusible. Not affected by acids. C.c. same as andalusite. Hillswick in Shetland, Mount Battock, Tarfside (fig. 451), Botriphnie (Banffshire), Tyrol, St Gotthard, Bohemia, Pontivy in France.

462. Sillimanite, Ä'lSi.

Right prismatic; ooP 111’. Crystals fibrous, columnar, and radiating. Cl. macrodiagonal. H. =7; G. =3’2 to 3’26. Translucent; resinous; on cl. vitreous. Greyish, greenish, clove, or hair-brown. C.c. and chemical characters like cyanite. Tvedestrand, Norway; Chester and Norwich, Connecticut. Al 2 O 3 ,SiO 9 is thus trimorphous.

Monrolite, Xenolite, Bucholzite, Fibrolite, and Bamlite are varieties.

463. Topaz, 5AlSi + A1F 3 + SiF 2 .

Right prismatic. ooP (Jf) 124’ 17', 2P∞ (n) 92’ 42', oof2 (Z) 93’ 14', P (o). Crystals always prismatic (fig. 122), often hemimorphic. Cl. basal, perfect; fracture conchoidal. H. = 8; G. = 3 ’4 to 3 '6. Transparent; vitreous. Colourless, honey-yellow, amber, pink, asparagus-green, blue. Becomes electric by heat or friction, and the yellow colours become pink. B.B. infusible. Not affected by h. acid; by digestion in s. acid gives traces of fluorine. The formula requires 33’2 silica, 56’7 alumina, 17 ’5 fluorine. Part of the oxygen must be replaced by fluorine, as the total of the above is 107’4. Ben-a-bourd and Arran, Scotland; Mourne Mountains, Ireland; St Michael’s Mount, Cornwall; Siberia, Saxony, Bohemia, Connecticut, Australia, Ceylon, Brazil, Peru. The finest topazes are the blue from Scotland and Siberia, the pink, the yellow from Brazil, and the colourless from Peru. The last-named when cut may be distinguished at once from diamond by their electricity. Pyrophysalitc is a massive opaque cleavable variety from Falun. Pycnite is a columnar straw-yellow to reddish white variety from Zinnwald in Saxony and Durango in Mexico.

464. Staurolite, (Al, Fe) Si + (Fe, Mg) Si.

Right prismatic. α>P (τn) 128’ 42', Poo (r) 70’ 46', ooPoo (o), θf(p) (fig. 452). Twins common, as figs. 140, 144, 187, 453. Cl. brachydiagonal, perfect; fracture conchoidal to splintery. H. =7; G. — 3’5 to 3’8. Transparent to opaque; vitreous to resinous. Reddish brown; streak white. B. B. infusible. Not affected by h. acid, partially by s. acid.

C.c.: silica 30, alumina 48*5, with 5*5 iron peroxide, 12‘5 iron protoxide, 3 5 magnesia; often impure. Bixeter Voe and Unst in Shetland, Boharm and Marnoch in Banffshire, St Gotthard, Greiner in Tyrol, Finistère, Urals, and North America. Xantholite is a yellow variety from Urquhart (Inverness).

465. Sapphirite, 4Mg, 5A1, 2Si.

Oblique prismatic; granular. H. — 7 to 8; G. — 3*4 to 3’5. Vitreous; pale blue or green; translucent; dichroic. C.c.: alumina 63*2, magnesia 19*3, silica 14*9. Fiskenaes in Greenland.

Tourmaline Group.

466. Tourmaline, ⅛ 1 Si + RSi.

Rhombohedral; R 133 10'. Crystals of 0R(⅛ z ),-⅜Rj usually long prismatic, and striated (fig. 45, and 249 to 252). Generally hemimorphic; also radiating and fibrous; fracture conchoidal to uneven. H.—6*5 to 7*5; G. —3 to 3*3. Black varieties opaque, others transparent; vitreous. Generally black; but colourless, yellow, brown, blue, green, and rose-red; streak white. Different colours often disposed in layers parallel to the axis; and portions of one crystal differing also in colour along the axis. By friction acquires positive electricity; and becomes electrically polar when heated. Powder insoL in h. acid; imperfectly in s. acid. C.c. complex, but all with water and fluorine, some with boracic acid. Coarse black columnar varieties, called Schorl, very common in granite and gneiss. Black occur at Portsoy in Banff, Clova, Cabrach, and Rubislaw in Aberdeenshire, Bovey in Devonshire, St Just in Cornwall, in Greenland, Arendal, Tyrol, and North America; blue or Indicolite at Utö in Sweden; green at Glen Skiag in Cromarty. Crystals ruby-red within, surrounded by green or red at one extremity and green at the other, also blue and pink, at Albany, Paris, and Hebron in Maine. Currant-red or Rubellite in India and Ceylon, also in Siberia and Brazil.

467. Datholite, 0aδ + 0aSi 2 + 0.

Oblique prismatic, C 89° 51'. α>P {g) ∏5 β 22', α>P 0 2 (f) 76’ 38', P (P) 120’, - P°oo (a) 45’ 8', a>P 0 ∞ (s), 2P e ∞ (o) (fig. 454); or rhombic with b :/90", b·.a 135’, b.c 141’ 9', and f·.g 160’ 39'. Fracture uneven, or conchoidal. H. — 5 to 5*5; G.— 2 *9 to 3. Transparent or translucent; vitreous. Colourless and tinted greenish, yellowish, or pink. In closed tube yields water. B.B. intumesces and melts easily to a clear glass, colouring the flame green; the powder gelatinizes in h. acid. C.c.: 38*1 silica, 21*6 boracic acid, 34*7 lime, and 5*6 water. Bishopton in Renfrew, Glen Farg in Perthshire (fig. 455), Salisbury Crags and Corstorphine Hill near Edinburgh, Arendal, Utö, Andreasberg, Seisser Alp, Connecticut, and New Jersey. Figs. 238, 239 are pseudomorphs of quartz after datholite termed Haytorite.

468. Euclase, 201Si + ÀÏH.

Oblique prismatic, C 79’ 4P. α>P c 2 (s) 115’; 3P c 3 (∕) 105’49'. Crystals specially of α>P e 2, α>P β oo (T), 3P i 3. Cl. clinodiagonal, perfect; very brittle and fragile; fracture conchoidal.

H. =7*5; G. =3 to 3*1. Transparent; splendent; vitreous.

Mountain-green, passing into blue, yellow, or colourless. B.B. intumesces, becomes white, and melts in thin splinters to a white enamel. Not affected by acids. C.c.: 42 silica, 35 alumina, 18 glucina, 6 water. Peru and Brazil, and Southern Urals. Cannot be used as a gem on account of its brittleness; whence its name.

469. Homilite.

Oblique prismatic, C 89’ 21'. Η. — 5*5; G. — 3*28. Black and brownish black. Vitreous. C.c.: 27*28 lime, 16*25 protoxide of iron, 31*87 silica, 18*1 boracic acid. Stokö and Brevig (Norway).

470. Botryolite.

Fine fibrous, botryoidal, or reniform. Snow-white to hair-brown. Chemical and physical characters like datholite, but 10*64 of water,—being 2 equivalents. Arendal.

471. Gadolinite, (Ÿ, 0e, Fe) a Si.

Oblique prismatic, C 89" 28'. ∞P 116’; P 120" 56' (fig. 458). Fracture conchoidal, or splintery. H. = 6 *5 to 7; G. = 4 to 4 *4. Translucent on the edges; vitreous to resinous. Black; streak greenish grey. Β.Β. the conchoidal (vitreous) varieties incandesce; gelatinizes in h. acid. C.c.: 36 to 51 ιrttria, 10 to 15 iron protoxide, 5 to 17 protoxide of cerium with anthanum, 0 to 12 glucina, and 25 to 29 silica. Hitterö in Norway, Ytterby, Broddbo and Finbo near Falun.

Epidote Group.

472. Zoisite, 4Ca, 3A1, 6Si + H.

Right prismatic. ooP 116" 26'; ooi s 2 145’ 24'; ∞Γ3 156’ 40'; P∞ 122’ 4'; 2?« 1116' (fig. 459). Cl. brachydiagonal, perfect. H. - 6; G. -3*2 to 3*4. White, brownish grey, and dark green. B.B. intumesces, and forms a white or yellow porous mass; and on the edges fuses to a clear glass. C.c.: 29*8 alumina, 24*35 lime, 2*8 oxide of iron, 40*3 silica, and 2*1 water. Glen Urquhart, Dalnain, and Allt Gonolan, Inverness; Sterzing in Tyrol, the Sau Alp in Carinthia, the Urals, and Connecticut.

Thulite, peachblossom-red, from Souland in Thelemark (Norway), is similar.

473. Epidote, 40a, 3A1, 6Si + H.

Oblique prismatic, C 89’ 27'. ooP 0 oo(Jf), ooP 2 (o) 63’ 1', P°αo(Γ) 64’ 36', - P (n) 70" 25', -P∞ (r) 63’ 42', P (z) 70". Crystals complex, with many partial forms. Hemitropes united by T ; also columnar and granular. Cl. Μ, perfect; also T, forming 115’ 24'; fracture conchoidal to splintery. H. — 6 to 7; G. —3*2 to 3*5. Pellucid; vitreous. Green to yellowish grey. B. B. fuses and swells to a dark brown slag; after fusion soluble with gelatinization in h. acid.

C.c.: 27*4 alumina, 8*5 iron peroxide, 23 *9 lime, 38*3 silica, 1*9 water. Shetland, Glenelginlnver∙ ness, Tilquilly in Aberdeen, in gneiss; in amygdaloid in Mull and Skye; in granite at Cassencary in Kirkcudbright; Arendal, Dauphiné, Greenland, the Urals, North America. Withamite from Glencoe is a red, strongly dichroic variety. Piedmontite or Manganese Epidote, brownish violet, from St Marcel, has 20 per cent, of manganese peroxide.

474. Allanite {Orthite, Cerine), R 3 Si 2 + RSi.

Oblique prismatic, C 65*. ooP (z) 70 48', P (n) 71⅜27 , - P ∖d) 96° 40', OP (Jf), P∞ (r), «Poo (T). Μ: Τ 115°, Τ:η 111° 21', T: d 130° 18'. Often massive or granular; fracture conchoidal. H. = 6; G. = 3 ’ 4 to 3 ’ 8. Translucent on edges; vitreous to resinous. Black to brown or greenish; streak brownish grey. B. B. froths and melts to a brown glass. Gelatinous with h. acid. C.c.: 12 to 18 alumina with peroxide of iron, 13 to 26 oxide of cerium and lanthanum, 2 to 12 yttria, 4 to 20 protoxide of iron, 30 of silica. Small crystals common in the syenitic granites of Scotland; as at Lairg, Boat of Garten (fig. 463), Aboyne, and Griffel. In limestone at Urquhart (fig. 462), Greenland, Hitterö and Snarum, Thuringia, Pennsylvania, New Jersey. Orthite (massive) at Finbo, Kragerö, and Falun. Cerine (granular) at Riddarhyttan. Pyr∙ orthite has carbonaceous matter. Bodenite is a variety.

475. Idocrase, 3(Ca, Mg) 3 Si + 2AlSi.

Pyramidal; P (c) 74° 27' (figs. 464 to 466). Crystals ∞P (d),

∞Poo (J∕), P (c), OP (p), Poo (o) 56° 29', ooP2 (∕). Prismatic, striated; also granular; fracture uneven. H. = 6 - 5;

G. = 3 ’ 35 to 4. Pellucid; vitreous to resinous. Brown, green, yellow; streak white. B.B. fuses easily, with intumescence, to a green or brown glass. Partially sol. in h. acid; after ignition totally, gelatinizing. C.c.: alumina 16, peroxide of iron 7, lime 34, silica 38. Glen Gairn and Crathie, Aberdeenshire, in limestone; Broadford, Skye; Wicklow and Donegal, Ireland; Egg, Norway; Mussa, Piedmont; Vesuvius; Wilui river, near Lake Baikal (fig. 463). Cyprine from Thele-

mark is azure-blue, from copper.

Olivine Group.

476. Forsterite, Mg 2 , Si.

Right prismatic. Like olivine (sp. 478). H. = 6 to 7; G. = 3 , 2 to 3 ’ 3. Vitreous; transparent. White, waxyellow, greenish; streak white. C.c.: magnesia 57 ’ 1, silica 42 - 86. Vesuvius.

Boltonité, red, is from Massachusetts.

477. Fayalite, Fe 2 Si.

Right prismatic; n: n' 49° 36' (fig. 467). Massive. Cl. rectangular. Black, greenish, or brownish. Metallic to resinous; fracture conchoidal; magnetic. H. = 6 - 5; G. = 4 to 4Ί. C.c.: protoxide of iron 70 ’ 5, silica 29 ’ 5. Mourne Mountains, Ireland; Fayal, Azores.

478. Chrysolite {Olivine, Peridote), (Fe, Mg) 2 Si.

Right prismatic. P (e) 85° 1 6' and

139° 54'; middle 108° 30'. ∞P {n) 130° 2', P∞ {d) 76° 54', 2P∞ {k) 80° 53', ooPoo (Jf) (fig. 468). Also massive. Cl. brachydiagonal, perfect; fracture conchoidal.

H.=6∙5 to 7; G.=33 to 3’5. Transparent; vitreous. Olive-green, yellow, brown, and colourless. B.B. infusible. Soluble, with gelatinizing, in acids. C.c.: 47 magnesia, 12 protoxide of iron, 40 silica. Talisker in Skye, Haalival in Rum, Elie in Fife, Unkel on the Rhine, Vesuvius, Esneh in Egypt, Brazil. Hyalosiderite, brown and yellow, with metallic lustre and 30 per cent, protoxide of iron, is from the Kaiserstuhl in the Breisgau.

479. Tephroite, Mn 2 Si.

Right prismatic; granular, with rectangular cleavages. Ash-grey, rose-red. Adamantine; translucent. H. = 5 - 5 to 6; G. = 4 to 4’1. C.c.: protoxide of manganese 70 ’ 2, silica 29 ’ 8. Franklin and Sparta in New Jersey.

480. Knebellite, Fe 2 Si + Mn 2 Si.

Massive. Grey, brown, green, black. Glistening; brittle. H. =6 - 5; G. =3 ’ 71. C.c.: protoxide of iron 35’5, protoxide of manganese 35, silica 29 ’ 5. Ilmenau, Dannemora in Sweden.

481. Monticellite, Ca 2 Si + Mg 2 Si.

Right prismatic. P (∕) 110° 43' and 97° 55', α>P (s) 98° 7', α>P2 (n) 133° 6', Poo {k) 81° 57', ⅛Poo (h) 120° 8', P2 (e) 141° 47' and 82°, α>foo (δ) (fig. 469). Vitreous. Grey, yellowish and greenish, and white; streak white. Translucent. H. = 5 to 5’5; G. =3 to 3’25. C.c.: lime 35, magnesia 21 - 9, protoxide of iron 5‘6, silica 37 ’ 5. Sol. in h. acid, gelatinizing. Somma (Milan).

482. Chondrodite {Humite), ⅛ 5 Si 2 .

Right prismatic. P middle edge 156° 38', polar edges 131° 34' and 54° 28' (figs. 470 to 472). Crystals monoclinic in habit, often granular-massive. H. = 6 , 5; G. = 3 ’ 15 to 3 ’ 25. Translucent; vitreous to resinous. Yellow, red, brown, green, and black; streak white. B. B. infusible. Decomposed by acids. C.c.: silicate of magnesia, with 2 to 3 of fluorine. From limestone on Loch Ness (?); Pargas, Finland; Gallsjo and Aker, Sweden; New York; Sparta, New Jersey. Humite, from Somma.

483. Lievrite, 3(Fe, Ca) 2 Si + FeSi + H.

Right prismatic. P (o) polar edges 139° 30' and 117° 27'; ∞P 112°38', Poo (i f) 112° 49', ∞P2 (s) 106° 15'. Crystals (fig. 124) are long-prismatic and vertically striated; also radiated, columnar, or fibrous; brittle. H. = 5 ‘5 to 6; G. = 3 ’ 9 to 4 ’ 2. Opaque; resinous or imperfect metallic. Brownish or greenish black; streak black. B.B. fuses easily to a black magnetic globule. Sol. in h. acid, forming a yellow jelly. C.c.: 29’3 silica, 19’6 iron peroxide, 35"2 iron protoxide, 13’7 lime, and 2 ’ 2 water. Rio in Elba, Fossum, Kupferberg, Rhode Island, and Greenland.

484. Cerite (Ce, β) 2 Si + 0.

Hexagonal; OP; ooP; in low six-sided prisms. Generally fine-granular; fracture uneven, splintery; brittle. H. =5*5; G. =49 to 5. Translucent on the edges; dull, adamantine, or resinous. Clove-brown, cherry-red, or pearl-grey. Sol. in h. acid, leaving gelatinous silica. C.c.: 20’5 silica, 73 5 protoxide of cerium (with didymium and lanthanum), and 6 water. Bastnaes near Riddarhyttan.

485. Galmei, Zn a Si + 0.

Right prismatic, and hemimorphic; 2P2 {P) with polar edges 101° 35' and 132’ 26', ∞P {d) 103° 50', Poo (o) 117° 14', P∞ (Z) 128° 55' (fig. 46); common form ∞Poo (s), ∞P, poo. Also columnar, fibrous, granular, and earthy. Cl. prismatic along ooP, very perfect; along Poo perfect. H. = 5; G. = 3 3 to 3 - 5. Transparent to translucent; vitreous and pearly. Colourless or white, but often light grey, also yellow, green, brown, and blue; becomes electric by heat. B.B. decrepitates slightly, but is infusible; with cobalt solution blue and partly green; readily soluble in acids, and S [elatinizes. C.c.: 25 silica, 67'5 zinc oxide, and 7'5 water. Wan-ockhead, Mendip Hills, Matlock, Raibl and Bleiberg in Carinthia, Aix-la-Chapelle, Iserlohn, Nertchinsk, Pennsylvania, Virginia. Used as an ore of zinc.

Willemite Group.

486. Willemite, Zn a Si.

Rhombohedral; R 116° 1'. Cl. basal, and prismatic, ooR; brittle. H. =55; G. =3 - 9to l - 2. White, yellow, brown, and red. Vitreous lustre. C.c.: oxide of zinc 73, silica 27. Altenberg, Liège, Greenland, New Jersey.

487. Troostite, Znè’i + MnSi.

Rhombohedral; R 116’. Cl. prismatic, ∞P2; brittle. H. =5 ’ δ; G. — 4Ί. Asparagus-green, grey, and reddish brown. Vitreous. C.c.: oxide of zinc 58, oxide υf manganese 13, silica 28. New Jersey.

488. Centrolite (PbMn) Si.

Right prismatic; »P 115’ 18'. Form ∞P, P, ∞f∞. H. — 5; G. =6'2. Red-brown. Cl. prismatic; splendent on P. Southern Chili

489. Phenacite, Gl 2 Si.

Hexagonal and tetartohedral; R (p) 116’ 36' (fig. 473). Crystals R, ooP2, ⅞P2. Twins with parallel axes, and intersecting.

Cl. R, and ∞P2; fracture conchoidal. H. =7’5 to 8; G. = 2 - 97. Transparent or translucent; vitreous. Colourless, and wine-yellow or brown when fresh, but colour soon lost on exposure. B.B. infusible; not affected by acids. C.c.: glucina 45 ’ 8, silica 54'2. Framont in Alsace, Takovaya in Urals, Miask, Durango in Mexico.

490. Dioptase, 0uSi + ≡≡.

Hexagonal and rhombohedral; R 125° 54',-2R(r) 95’ 28', ∞P2, - 2R⅝ (s) (fig. 474). Cl. R, perfect; brittle. H. = 5; G. = 32 to 3'3. Transparent or translucent; vitreous. Emerald-green, rarely verdigris-green or blackish green; streak green. C.c.: 38'7 silica, 50 copper protoxide, and 11'3 water. Altyn-Tiibeh in the Kirghiz Steppe, Murosh-naya, Copiapo.

491. Chrysocolla, CuSi + 2H.

Botryoidal or investing; brittle; fracture conchoidal. H. = 2 to 3; G. = 2 to 2 '3. Translucent; resinous. Verdigris-to emerald-green or azure-blue; streak greenish white. C.c.: 34 - 83 silica, 44 '94 copper protoxide, and 20 '23 water. Leadhills, Lackentyre in Kirkcudbright, Cornwall, Saxony, Hungary, Spain, Urals, Australia, Chili.

492. Bogoslovskite {Kupferblau).

Massive; fracture conchoidal; brittle. H. = 4 to 5; G. = 2 '56. Sky-to ultramarine-blue; streak smalt-blue, and shining. A silicate of copper, with 45'5 per cent, copper oxide. Schapbach Valley in Baden, Bogoslovsk in the Urals. Demidowite may be the same.

Garnet Group.

493. Garnet, ft 3 Si 2 + RSi.

Cubic; most common forms α>O and 202 (figs. 33, 40, 60, 475). Also granular. Cl. dodecahedral; fracture conchoidal, or splintery. H. —6'5 to 7'5; G.=3∙5 to 43. Pellucid; vitreous or resinous. Rarely colourless or white; generally red, brown, black, green, or yellow. B. B. in general fuses to a glass, black or grey in those containing much fron, green or brown in the others, and often magnetic; imperfectly soluble in h. acid. C.c. exceedingly variable, but generally forming two series, according as R 2 O 3 is chiefly alumina or chiefly iron peroxide; and these are again divided according as RO is more especially lime, iron protoxide, magnesia, or a similar base. The more important varieties are—

(1) Lime-Alumina Garnet, Ca 3 Si 2 + AlSi, with 40 silica, 23 alumina, and 37 lime. To this subdivision belong—

(a) Water Garnet.— Colourless to white. Craig Mohr, Aberdeen; Thelemark in Norway.

(δ) Grossular. — Oliveto gooseberry-green. Craig Mohr; Wilui river; America.

(c) Cinnamon Stone.— Hyacinth-red to orange-yellow. Glen Gairn (Aberdeen), Allt Gqnolan and Ord Ban (Inverness), Ceylon, Wermland. Romanzowite, from Kimito (Finland), is the same. This variety when polished is often sold as Hyacinth. {d) Common Lime Garnet.— Here one half of the alumina is replaced by iron peroxide. Colours red, brown, yellow. Piedmont, Vesuvius, the Urals.

(2) Magnesia-Alumina Garnet ; RO chiefly magnesia. Arendal.

(3) Manganese-Alumina Garnet·, RO = MnO; reddish-brown. Spessart (Bavaria), Sweden.

(4) Magnesia-Iron-Lime· Ahιmina Garnet, Pyrope.— (?olour portwine to purplish red. Elie in Fife, Zöblitz in Saxony, Bohemia.

(5) Iron-Alumina Garnet, Almandine, Noble Garnet. — Columbine-red, inclining to violet, blood-red, and reddish brown. Common in mica-slate, gneiss, and granite. Shetland, Ross, Inverness, Aberdeen, Falun, Arendal, Tyrol, the Urals, North America, Pegu, and Ceylon.

(6) Lime-Chrome-Alumina Garnet, Ca 3 Si 2 + (Gr, Al)Si, Uwaro wite. Emerald-green; with 22 per cent, chrome oxide. Bissersk and Kyshtimsk in the Urals, India, and California.

(7) Lime and Iron Garnet, Ca 3 Si 2 + ⅛⅛, Si. This includes—

(a) Common Iron-Garnet, Rothoffite, Allochroite. — Subtranslucent or opaque. Green, brown, yellow, or black; with white, grey, or yellow streak. Sweden and Arendal.

{b) Melanite. — Black; opaque; in thin splinters translucent; streak grey; slightly magnetic. Albano near Frascati, Vesuvius, France, Lappmark.

(c) Colophonite.— Yellowish-brown to pitch-black, also yellow or red; resinous; streak white. G. =3'43. Arendal.

The red varieties, when cut en cabochon, are termed Carbuncles.

494. Axinite, (Al, B) Si + 2(0a, Fe)Si.

Anorthic. Crystals unsymmetrical, u: P 135’ 31'; u·.r 115’ 38', P.r 134’ 45' (figs. 136, 137). Cl. distinct along planes truncating the sharp edges between P and u andP and r. H. =6'5 to 7; G. = 3'2 to 3 ’ 3. Pellucid; vitreous. Clove-brown, inclining to smoke-grey or plum-blue; but often cinnamon-brown in one direction, dark violet-blue in a second, and pale olive-green in a third {trichroism). B.B. colours flame green; intumesces, and fuses easily to a dark green glass, becoming black in the ox. flame; ≡ot sol. in 1∣. acid till after ignition, when it gelatinizes. C.c.: 45’9 silica, 5 ’ 9 boracic acid, 17‘5 alumina, 9'3 iron (with manganese) protoxide, and 21'4 lime. Botallack and other mines in Cornwall, Bourg d’Oisans in Dauphiné, Kongsberg, Arendal, Nordmark in Sweden, Pyrenees, St Gotthard, Tyrol, Thum in Saxony, Urals, and North America.

495. Danburite (Ca, B) 2Si.

Right prismatic. α>P {I) 122’ 52', oof 2 {e) 94’ 52', P∞ {d) 97’ 7', 4foo {w) 54’ 58', 0P (c), P {o), 2p2 {r), oop∞ {a), oof4 {n).

Cl. basal; fracture uneven to subconchoidal; vitreous to greasy lustre. H. =7 to 7'5; G. =2'986 to 3 021. Pale yellow to reddish brown. Translucent; brittle. C.c.: 22'76 lime, 28'46 boracic acid, 48 - 76 silica. Danbury in Connecticut, Russell in New York.

Helvine Group.

496. Helvine, MnS + 3R 2 Si.

Cubic and tetrahedral. ⅛ or - s 5 - (fig. 64 and with 66). Im-

Δ Δ Δ

bedded or attached. Cl. octahedral. H. =6 to 6 '5; G. = 31 to 3'3. Translucent on the edges; resinous. Wax-yellow, siskingreen, or yellowish brown. B. B. in the red. flame fuses with intumescence to a yellow obscure pearl; sol. in h. acid, evolving sulphuretted hydrogen, and gelatinizes. C.c.: 34 silica, 10 glucina, 8 iron protoxide, 43 manganese protoxide, and 5 sulphur. Schwarzenberg in Saxony, and near Modum in Norway.

497. Danalite, 3f 2 Si + ZnS.

Cubic. In octahedra, with striated dodecahedral planes. H. — 5'5 to 6; G. =3'43. Vitreous to resinous. Flesh-red to grey; streak lighter. Translucent; brittle. C.c.: protoxide of iron 29, of manganese 6'5, of zinc 19, silica 31'5, sulphur 5'5. Rockport in Massachusetts.

498. Eulytine, δi 2 Si 3 .

Cubic and tetrahedral. and - ^^S~^ . The crystals (fig. 66) Δ Δ small, and often with curved faces; fracture conchoidal. H. = 4 '5 to 5; G. =5'9 to 6'1. Transparent and translucent; adamantine. Clove-brown, yellow, grey, or white; streak white or grey. C.c.: 16'2 silica and 83'8 bismuth peroxide. Schneeberg and Braunsdorf near Freiberg.

Scapolite Group.

499. Sarcolite, 8Ca, 3À1, Na, 9Si.

Pyramidal. P 102’ 54'; ooPα>; OP; P, and other faces as in fig. 480, many of the faces being alternately hemihedral. H. =5’5 to 6; G. = 2 , 93. Vitreous. Grey to rose-red. Translucent; very brittle. C.c.: alumina 21’5, lime 32 ’ 4, soda 3’3, silica 40’5. B.B. fuses to a white enamel; gelatinizes with acids. Somma.

500. Meionite, 6(da, Na), 4A1, 9Si.

Pyramidal. P (o) 63° 42'; Poo (i); ooP (a); ooP (δ) (fig. 481). Cl. macrodiagonal. H. =5’5 to 6; G. = 26 to 2’74. Vitreous. Colourless or white.

Transparent. Much cracked. C.c.: 31’9 alumina, 26 ’ 2 lime, 41’9 silica. Gelatinizes in acids. Somma.

501. Mizzonite, 6(0a, Na), 4Â1, 15*Si.

Pyramidal; P 64* 4' (fig. 482). Similar to meionite. C. c.: alumina 23’8, lime 8 ’ 8, soda 9 ’ 8, silica 547. Insoluble in b. acid. Somma.

502. Scapolite, 3(Ca, Na)Si +¾ 2 Si 8 .

Pyramidal. P 63* 42'; »Poo; P; ooP; also massive. Cl. coPoo, perfect; and α>P. H. —5 to 5'5; G. =2’6 to 2 ’ 8. Transparent or translucent; vitreous, pearly, or resinous. Colourless, but also pale grey, green, yellow, or red. B. B. melts with effervescence to a vesicular glass; in the closed tube may show traces of fluorine; with solution of cobalt becomes blue. Sol. in h. acid. C.c.: 49 silica, 28 alumina (with iron peroxide), and 23 lime (with soda). Tiree (Scotland), Arendal, Tunaberg, Pargas, Massachusetts, and New York. Known by its rectangular cleavage, resinous lustre on fractured surfaces, and action B. B. Dipyre, P 64° 4', is a variety.

503. Mellilite (Humboldtilite), 2(Ca, Mg)Si 2 + (⅛1, Fe)Si.

Pyramidal. P 65’ 30'; OP; »Poo. Cl. basal, perfect. H. =5 to 5'5; G. =2 ’ 91 to 2’95. Translucent on edges; vitreous to resinous. Honey-yellow, orange-brown, and yellowish white. C.c.: 32 lime, 7 magnesia, 9 alumina, 7 iron peroxide, 40 silica. Capo di Bove, and Vesuvius.

504. Gehlenite, (Ca, Fe) 3 Si + (Al, Fe)Si.

Pyramidal. P. 59’; OP; ooPα>; ooP3; 2P. Cl. basal. H. =5’5 to 6; G. ≈2 , 9 to 3’1. Translucent on edges. Dull resinous. Mountain-, leek-, or olive-green, and liver-brown. C.c.: 22 alumina, 5 iron peroxide, 35 lime, 4 magnesia, 31 '4 silica. Monzoni in the Fassa Valley.

Nepheline Group.

505. Leucite, Ä1, Si 8 + KSi.

Pyramidal. Combination of the ditetragonal pyramid (*) with the tetragonal pyramid z b), and 2P∞ (u) with ooP(m). Hemitropes united by (u). Fracture conchoidal. H. — 5 ’ 5 to 6; G. = 2 - 4 to 2 ’ 5. Transparent to translucent on the edges; vitreous, inclining to resinous. Colourless, but greyish, yellowish, or reddish white; streak white. B. B. infusible; with cobalt solution becomes blue. Sol. in h. acid, without gelatinizing. C.c.: 54’9 silica, 23’6 alumina, and 21’5 potash. Abundant in the lavas of Vesuvius, the tufas near Rome, and the peperino of Albano; also at the Kaiserstuhl, and near Lake Laach. Readily distinguished from analcime by its infusibility, and by never showing faces of the cube.

506. Nepheline (Elaeolite), ÀlSi + 4(Na, K)Si.

Hexagonal. P 88’ 10'. ooP, 0P, P common; also fig. 485. Crystals imbedded, or in druses; also massive-granular; fracture conchoidal, or uneven. H. =5’5 to 6; G. =2 ’ 58 to 2 ’ 64. Transparent or translucent; vitreous and resinous. Colourless or white (nepheline); or opaque, dull resinous, and green, red, or brown (elaeolite). B.B. melts difficultly (nepheline), or easily with slight effervescence (elaeolite), into a vesicular glass. Sol. and gelatinizes in h. acid.

C.c.: 41’2 silica, 35‘3 alumina, 17 soda, 6’5 potash. Nepheline at Monte Somma, Capo di Bove, Katzenbuckel in the Odenwald, Aussig, and Lusatia. Elaeolite in the zircon syenite at Laurvig, Fredriksvärn, Brevig, and Miask.

Davine, with ⅜P 51° 46', seems only a variety; as also Cancrinite, bright blue, and with some carbonate of lime.

507. Microsommite, RSi+AÎSi + NaCl.

Hexagonal. ooP;0P; ooP2;ooP$. Cl. ooP. H.=6;G.=2’42 to2∙53. Colourless to yellow; lustre silky. Somma and Vesuvius.

508. Sodalite, 3(AlSi + NaSi) + NaCl.

Cubic; ooO, and fig. 486; generally distorted; also massive and granular. Cl. ∞O; fracture conchoidal or uneven. H. = 5·5; G.=2∙13 to 2∙29. Translucent; vitreous. White, grey, and rarely green or blue. C.c.: 37 silica, 31 8 alumina, 19*2 soda, 4 7 sodium, and 7 ’3 chlorine. Greenland, Vesuvius, Ilmen Hills, Fredriksvärn, and Litchfield in Maine.

509. Nosean, 3(AlSi + NaSi)

+ NaS.

Cubic; and granular. H. = 5 ∙5; G. = 2 ∙28 to 2 ∙40. Translucent; vitreous to resinous. Ash or yellowish grey, sometimes blue, brown, or black. C.c.: 36 silica, 31 alumina, 25 soda, and 8 sulphuric acid. Lake Laach, and Rieden near Andernach, on the Rhine. Occurs in phonolites, in minute crystals.

510. Hauyne, 2(AlSi + J⅜aSi) + ÔaS.

Cubic; chiefly ooθ; also fig. 487; but more common in grains. Cl. ooO. H. =5 to 5·5; G. =2∙4 to 2'5. Semitransparent or translucent; vitreous or resinous. Azure-or sky-blue; streak bluish white. C.c.: 34’2 silica, 28 '5 alumina, 11 ’ 5 soda, 4 ’ 3 potash, 10’4 lime, and 11 *1 sulphuric acid. Vesuvius, Mount Vultur near Melfi, the Campagna of Rome, and Niedermendig near Andemach.

511. Lapis-Lazuli.

Cubic; Oα>; generally massive, granular. H.-5-5; G.-2∙38 to 2’42. Translucent on edges; dull resinous or vitreous. Ultramarine, or azure-blue; streak light blue. B.B. fuses readily to a white porous glass. In h. acid the powder is dissolved and gelatinizes, evolving sulphuretted hydrogen. C.c.: 45’50 silica, 5'89 sulphuric acid, 31’76 alumina, 9’09 soda, 3’52 lime, 0’86 iron, 0’42 chlorine, 0’95 sulphur, 0Ί2 water. Near Lake Baikal, China, Tibet, Tartary, Monte Somma, and Chili. It is used for ornamental purposes, and in the preparation of ultramarine. The colour both in it and hauyne seems due to some compound of sulphur with sodium and iron.

Mica Group.

512. Biotite (Magnesia-Mica), Al 2 Si 3 + (Mg, K, Fe) 2 Si 8 .

Oblique prismatic, C 89’ 59'. 0P (c), 98" 4Γ P (τn),-⅜P (o), ooP c oo (b), fαo (r), - ⅜P c 3 (z). Cl. basal, perfect; sectile; thin plates elastic. H.—2’5 to 3; G. =2’85 to 2’9. Transparent, but often only in very thin plates. Generally uniaxal, sometimes with divergence =~ 56°. Metallic, pearly. Usually dark green, brown, or black; streak greenish grey or white. B. B. difficultly fusible to a grey or black glass. Completely soh in concentrated s. acid, leaving white pearly plates of silica. C.c.: 39 silica, 17 alumina, 10 iron protoxide, 20 magnesia, 9 potash. Hillswick, Shetland, in gneiss; Sutherland, Ross, Inverness, in limestone; Skye and Fife in trap; Pargas, Bodenmais, Greenland, New York. Rubcllan is a decomposed variety.

513. Haughtonite, (Al,Fe) Si + (Fe, ⅛) a Si.

Oblique prismatic. Cl. basal, perfect. H. =3; G. — 3 ’ 1. Vitreous to adamantine. Chocolate-brown to black. Weathers pale green and ochry. Difficultly soluble in acids. B.B. fused with difficulty to a highly magnetic bead. C.c.: silica 36, alumina 18, ferric oxide 4'5, ferrous oxide 18, magnesia 9, potash 8, water 3. Common in the granites of Scotland. Black Forest, Harzburg, Tyrberger.

514. Lepidomelane, (Al,Fe) Si + (Fe, K)Si.

Oblique prismatic. Cl. basal, perfect; brittle. H. =3; G. =2'97. Vitreous; transparent to opaque. Rich brown to raven-black. B. B. fuses easily to a black feebly-magnetic bead. Sol. in h. acid, leaving pearly scales of silica. C.c.: 37 silica, 17 alumina, 24 iron peroxide, 3 protoxide of iron, 8 potash, 10 magnesia, 4 water. Rarely in gneiss, Scotland; common in granite, Ireland; and Pers-berg, Sweden.

515. Anomite, 12Mg, 3Ä1, 2K, H, 12Si.

Oblique prismatic, c :m 98° 42'. Form c, m, o, b (see fig. 488); divergenceof optic axes 12°to 16°. Monroe(New York), Lake Baikal.

516. Phlogopite, (iR 3 + ⅛⅛) S*i 8 .

Oblique prismatic. OP (c), P(τn),-⅜P (o), α>Poo (δ). c:m 98° 30' to 99°. Cl. basal, perfect. H. =2'5 to 3; G. — 2'75 to 2’97. Pearly to submetallic. Yellowish brown with copper-like reflexion; also green, white, and colourless. Transparent. Divergence of optic axes 3° to 20°. C.c.: 14 alumina, 2 protoxide of iron, 28 magnesia, 8 ’6 potash, 2 , 57 fluorine, 41 silica. B. B. whitens, and fuses on edges. Deconιposed by s. acid, leaving the silica in scales. Pargas (Finland), Fassa Valley, New York, Canada, Ceylon. Characteristic of serpentine and of dolomitic limestones.

517. Zinnwaldite.

Oblique prismatic. Forms as in figs. 490, 491; also 2P∞ (H) and 3P c 3 (x). m: c 98° to 99°. Divergence of optic axes 65°. G. = 2'82 to 3’2. C.c. similar to muscovite (sp. 519), but with 4 to

8 fluorine, 2 to 5 lithia, and traces of rubidium, caesium, and thallium. Altenberg and Zinnwald, St Just and Trewavas in Cornwall. Cryophyllite from Cape Ann in Massachusetts is similar.

518. Lepidolite.

Oblique prismatic. Forms like muscovite. Divergence of optic axes 50 t to 77°. Cl. basal, perfect. H. = 2 , 5 to 4; G. = 2'84 to 3. Often massive; scaly granular, coarse or fine. Lustre pearly. Colour rose-red, violet, lilac, yellow, greyish white. Contains 5 to 6 per cent, lithia, with rubidium, caesium, and thallium, also fluorine. B. B. colours flame red. Mourne Mountains, Rozena (Moravia), Utö (Sweden), Ekaterinburg, Maine.

519. Muscovite (Muscovy-Glass), 3AlSi + XSi.

Right prismatic, with monoclinic habit. 0P (c); α>P (M)∙, α>P c oo (5); P (mi); 2P c oo (y). α>P nearly 120°. Twin-face c. Cl. basal, perfect; elastic. Angle of optic divergence from 44° to 77°. Metallic, pearly. Colourless, and tinged of various shades to black. B. B. fuses to an opaque enamel. Not affected by acids. C.c.: 36'6 alumina, 11 - 8 potash, 45 Ί silica, 4 - 5 water, with traces of fluorine. Shetland, Loch Glass in Sutherland, Glen Skiag (crystals 15 inches in length) and Struay Bridge in Ross, Aberdeen, Cornwall, St Gotthard, Norway, Sweden, Siberia. Crystals over a yard in diameter in China, where it is used for windows. Fuchιte, bright green, has 6 per cent, of chrome oxide. Margarodite contains 4 to 6 water. Gilbertitc, Cornwall, may be different.

520. Paragonite (SWα-3fιcα), 3'Al 2 Si 3 + (Na, S)Si.

Massive; foliated. Lustre pearly. H. = 2'5 to 3; G. —2’78 to2∙9. Yellowish, greyish, and greenish. C.c.: 40Ί alumina, 6 1 soda, 47 *75 silica, 4'6 water. Monte Campione, St Gotthard.

521. Sandbergekite (Baryta-Mica).

White minute scaled aggregates. G. -2'894. C.c.: 30'2 alumina, 4'9 magnesia, 5'9 baryta, 7'6 potash, 42 6 silica, 4 43 water. Pfitsch Valley in Tyrol, and the Swiss Alps.

522. Margarite (Lime-Mica).

Right prismatic. Cl. basal perfect. H. =35 to 45; G. — 2'99 to 3‘1. Lustre of cl. pearly. Lateral planes, vitreous. Snow-white, reddish white, and. pearl-grey. Laminae brittle. Optic axial angle 109’ to 129°. C.c.: 51'2 alumina, 11'6 lime, 2 ’ 6 soda, 301 silica, and 4'5 water. Greiner in Tyrol, Naxos, Asia Minor, Greece, Pennsylvania, North Carolina. Diphanite is similar.

523. Euphyllite (⅜ft 3 + gft) a Si 8 + ⅛H.

Like muscovite, but laminae not easily separable. H. — 3 '5 to 4 '5; G. =2'83 to 3. Lustre of cl. pearly to adamantine. White to colourless. Transparent to opaque. Laminae brittle. Optic axial angle 71⅛°. C.c.: alumina 42'3, lime 15, potash 3'2, soda 5'9, silica 41 6, water 5'5. Unionville in Pennsylvania.

524. Clintonite, (∣ft 3 + ∣Al) a Si + ⅛f≡.

Oblique prismatic; in hexagonal tables, or massive foliated. Cl. basal, perfect. H. = 5 to 5'5; G. =3'15. Translucent; pearly to metallic on the cleavage. Angle of the optic axes 3° to 13°. Reddish brown to yellow. C.c.: 39'7 alumina, 21Ί magnesia, 13 Ί lime, 19'2 silica, 2 protoxide of iron, 4'9 water. Amity and Warwick in New York. Brandisite is similar.

525. Xanthophyllite.

Oblique prismatic, C about 90°. Crystalline aggregates. Radiate lamellar. H. =4'5 to 6; G. =3'1. Lustre pearly. Colour yellowish to copper-red. Angle of optic axes 0° to 20°. C.c.: alumina 43'6, lime 13, magnesia 17'5, silica 16'9, water 5'1. Zlatoust.

526. Chloritoid, FeSi + AlH.

Right prismatic; in foliated crystals; brittle. Cl. basal. Lustre greasy to pearly. H. =5'5 to 6; G. =3'52 to 3'56. Dark green; streak greenish white. C.c.: 40 alumina, 27 protoxide of iron, 25 silica, 7 water. B.B. infusible, but becomes magnetic. Decomposed by s. acid. Hillswick in Shetland, Pregratten in Tyrol, Ekaterinburg, Canada.

527. Masonite.

Broad plates. H. =6'5; G. =3'53. Grey-green. Streak grey. Pearly to vitreous. C.c.: 26'4 alumina, 19 peroxide of iron, 16'7 protoxide of iron, 32'68 silica, 4'5 water. Middletown in Rhode Island.

528. Ottrelite, AI 2 Si 3 + 3(Fe, KIn)Si + 3⅛.

Thin hexagonal tables. Cl. parallel to the prismatic faces. H. — 5 , 5; G. =4'4. Translucent; vitreous. Greenish or blackish grey. C.c.: 24'3 alumina, 16'8 protoxide of iron, 11Ί protoxide of manganese, 43'4 silica, 5'65 water. Ottrez in the Ardennes (Luxemburg), Aste in the Pyrenees, Ebnat in Bavaria, Newport (Rhode Island), Vardhos (Greece).

529. Pyrosmalite, 7RSi + RCl a + 5H.

Hexagonal. P101° 34'; crystals ∞P, OP; tabular; also granular. Cl. basal, perfect; brittle. H. =4 to 4'5; G. — 3 to 3'2. Translucent to opaque; resinous, or metallic-pearly. Liver-brown to olive-green. C.c.: 35'5 silica, 27'5 iron protoxide, 21'5 manganese protoxide, 8 chloride of iron or manganese, and 7 '5 water. Nordmark in Sweden.

530. Astrophyllite, (R 3 , R) a Si j .

Right prismatic, with oblique habit. In long tabular prisms, and in stellate groups. Cl. basal, perfect. H. =3'5; G. — 3'33. Submetallic to pearly. Tombac-brown to gold-yellow. Pellucid. Axial divergence 118“ to 124°. C.c.: peroxide of iron 9'3, protoxide 23'6, protoxide of manganese 10, soda 3'9, potash 5'9, titanic acid 7 '90, silica 39 '2. Brevig, El Paso in Colorado.

Chlorite Group.

531. Chlorite, 2RSi + ħ 2 Al + 3H.

Hexagonal. P 106° 50'; crystals tabular of 0P, ∞P or 0P, P (fig. 493); often in comb-like or other groups; generally foliated andscaly. H. =1 to 1'5; G. —2'78 to 2'96. Leek-green to blackish green; streak greenish grey. C.c.: 21 alumina, 20 protoxide of iron, magnesia 18, silica 24, water 11. Tarfside, Bute, and Jura in Scotland. Cornwall, Cumberland, Wales, Fassa Valley, Urals, America.

532. Pennine, 4MgSi + Mg 3 AI + 5H.

Hexagonal, rhombohedral; R 65° 28'. Crystals chiefly very acute rhombohedrons, with or without the base. Lustre resinous. H. = 2 to 3; G. =2’6 to 277. Streak greenish white. B.B. exfoliates, becomes white, and fuses on the edges to a white enamel. Completely sol. in warm s. acid. C.c.: 33’6 silica, 14’4 alumina, 39 4 magnesia, and 12'6 water; but with 5 to 6 iron protoxide replacing magnesia. Scalpa in Harris, Glen Lochy in Perthshire, Zermatt in Valais, Tyrol, Ala di Stura in Piedmont, Mauléon in the Pyrenees. Lcuchtenbergite is the same. Kammererite, with 5 to 8 chromium sesquioxide, is violet-blue or green; Unst, Siberia, Pennsylvania. Rhodochrome and Tabergite are alsρ varieties.

533. Clinochlore ^Ripidolite), 3MgSi + Mg 3 Al + 40.

Oblique prismatic, C. 76° 4'. ∞P 121° 28'. OP: P 113° 59'; OP: 00P 192° 8'. Crystals - 2P, P, 4P c ∞, OP (n, m, t, P, fig. 494). Twins common; lustre vitreous or resinous. H. =2 to 3; G. =2 - 6 to 2'8. B.B. becomes white, and fuses on thin edges to a greyish yellow enamel. C.c.: 30'3 silica, 17'3 alumina, 40'3 magnesia, and 12Ί water. Edentian and Blair Athole in Scotland, Traversella in Piedmont, Akhmatovsk in Urals, West Chester in Pennsylvania. Corundophyll·ite, Epichlorite, and Kotschubeyite are varieties.

534. Pyrosclerite, (∣ft, ⅜R) 3 Si 3 +3H.

Right prismatic. Cl. basal, perfect; fracture uneven; brittle; sectile. H. =3; G. = 27 to 2’8. Pearly; translucent. Apple-, emerald-, and grey-green. C.c.: alumina 13'4, chrome oxide 1'4, protoxide of iron 3'5, magnesia 3Γ6, silica 37, water 11. PortoFerraio in Elba, China.

535. Chonicrite.

Massive; crystalline-granular and globular-radiated. H. = 2 '5 to 3; G. =2’91. Weak silky. White, with yellowish spots; greenish blue. C.c.: 17’1 alumina, 22 ’ 6 magnesia, 12‘6 lime, 35'7 silica, 9 water. B.B. fuses easily, with intumescence, to a grey glass. Decomposed by h. acid, with separation of silica. Colmonell (Ayrshire), Porto-Ferraio.

536. Pycnotrop.

Large grained aggregates. Cl. along two rectangular faces; fracture hackly, splintery. Greyish white to brown-red. Vitreous to greasy. H. =2 to 2 '3; G. =2’6 to 2'7. C.c.: alumina 29'3, magnesia 12'6, potash 4'4, silica 45, water 7'8. Waldheim in Saxony.

537. Thuringite, (⅛R, ¾ + ⅛(Al, Fe)) 4 Si 3 + 40.

Massive; scaly. H. = 2 to 2 '5; G. = 3 '2. Pearly. Olive-green to pistachio-green; streak paler. Very tough. Powder greasy. C.c.: alumina 16, peroxide of iron 14, protoxide of iron 33, silica 23, water 11. Schmiedefeld in Thuringia, Harper’s Ferry on the Potomac, Hot Springs in Arkansas.

538. Delessite, (Fe∣, Mgi) 2 Si 2 + (⅛l⅛, Fe τ ⅛)Si + 30 + 2MgS.

Massive; scaly. H. =2 to 2 - 5; G. = 2'6 to 2'89. Olive-green to dark green, passing to dark brick-red; streak light green. C.c.: alumina 16'3, protoxide of iron 12'6, magnesia 21, silica 31'5, water 15'8. Common in igneous rocks of Old Red Sandstone and Coalmeasure age in Scotland. Oberstein, Zwickau, Lagrève near Mielin.

539. Cronstedtite, FeSi + (Fe, l⅛g) 3 Si + 30.

Rhombohedral; radiated columnar. In tapering hexagons, and hemihedral (figs. 495, 496). Cl. basal, perfect; elastic. H. = 2'5; G. =3'3 to 3'5. Vitreous. Coal-black and brownish black; streak dark olive-green. C.c.: protoxide of iron 39, peroxide of iron 29, silica 22, water 11. Huel Maudlin in Cornwall, Przibram, Brazil {Sidcroschisolitc). Talc and Serpentine Group.

540. Talc, Mg 3 Si 4 + 0.

Right prismatic (?); rarely found in six-sided or rhombic tables; generally massive, granular, or scaly. Rarely fibrous. Cl. basal, perfect; soft, sectile, and flexible in thin plates. H. =1; G. =2'6 to 2'8. Transparent in thin plates, and optically binaxal; pearly or resinous. Colourless, but generally greenish or yellowish white to apple-or olive-green. Feels very greasy. B.B. emits a bright light, exfoliates, and hardens (H. =6), but is infusible; with cobalt solution becomes red. Not sol. in h. or s. acid before or after ignition. C.c.: 63 - 5 silica, 31'7 magnesia, and 4'8 water. Unst in Shetland, green; Cairnie in Aberdeenshire, brown; Greiner in Tyrol, Sala and Falun, the Pyrenees. Used as crayons, also for forming crucibles and for porcelain.

Steatite.— Massive. Grey, red, yellow, or green. Shetland, Sutherland, Portsoy, and near Kirkcaldy, Scotland; the Lizard Point, Cornwall; Briançon, Wunsiedel. Savage nations cut the steatite into culinary utensils.

Potstone is a mixture of talc, chlorite, and other minerals.

541. Picrophyll, 3RSi + 2H.

Right prismatic. H. = 2'5; G. =3'75. Dark green. Foliated, shining. C.c.: magnesia 30'1, protoxide of iron 6'9, silica 49'8, water 9'8. Sala in Sweden.

542. PiCROSMiNE, 2MgSi+0.

Right prismatic, but massive. Cl. 00P∞ perfect, less so in other directions; sectile. H. = 2'5 to 3; G. =2'5 to 2'7. Translucent or opaque; vitreous, but pearly on 00P∞. Greenish white, grey, or blackish green; streak colourless. Yields a bitter odour when breathed on; hence the name. C.c.: 55'8 silica, 36 Ί magnesia, and 8Ί water. Presnitz in Bohemia, and Greiner in Tyrol.

543. Monrad ite, 4(⅞Mg, ⅜Fe)Si + ft.

Massive, foliated, translucent, and yellowish-grey. H. = 6; G. = 3'27. C.c.: silica 55'2, magnesia 31'9, protoxide of iron 8'8, water 4Ί. B.B. infusible. Bergen in Norway.

544. Meerschaum, 2Mg 2 Si 3 + 4H.

Fracture earthy; sectile. H. = 2 to 2'5; G. =0'8 to 1 (when moist nearly 2). Opaque, dull. Yellowish and greyish white; streak slightly shining. Feels rather greasy, and adheres strongly to the tongue. C.c.: 54'2 silica, 24'7 magnesia, and from 9 to 21'7 water. Negropont, Anatolia, near Madrid and Toledo, Moravia, Wermland,

545. Aphrodite, 4MgSi + H.

Soft and earthy. G. =2'21. Milk-white; opaque. C.c.: 52'9 silica, 35'3 magnesia, 11'9 water. Lângban (Sweden), Elba.

546. Spadaite, Mg 5 Si β + 4H.

Massive; fracture splintery; sectile. H. =2'5. Translucent; resinous. Red, with white streak. C.c.: 57 silica, 31'6 magnesia, 11'4 water. Capo di Bove near Rome.

547. Gymnite.

Massive. H.=2to 3; G. = 1'9 to 2 2. Translucent; resinous. Dull orange-yellow. C. c.: 41 silica, 37 magnesia, 22 water. Tyrol, Passau, Texas, Barehills near Baltimore. Nickel Gymnite has 29 of nickel oxide, replacing the water. Unst, Texas, Pennsylvania.

548. Saponite, (FeCaMg) β Si β + (Al 3 Fe)Si + 13Ö.

Massive; sectile, and very soft. H. =1'5; G. =2'2to 2'3. White, orange-yellow, pale green, and reddish brown. Feels greasy; does not adhere to the tongue; falls to pieces in water. C.c.: silica 40'8, alumina 7'5, ferric oxide 3'9, magnesia 20'6, water 227. Occurs in all the above colours in the later igneous rocks of Scotland, commonly. Lizard Point and St Clear in Cornwall, and Dalecarlia in Sweden. Pimelite has 2'8 oxide of nickel.

549. Serpentine, 2¾Si + Mg⅛ 3 .

Crystallization uncertain; pseudomorphic after olivine, &c.; generally massive, and granular or fibrous; fracture flat-conchoidal, uneven, or splintery; sectile, and slightly brittle. H. = 3 to 3'5; G. = 2'5 to 2'7. Translucent to opaque; dull resinous. Green, grey, yellow, red, or brown; often in spots, stripes, or veins; streak white, shining. Feels greasy, and does not adhere to the tongue. In the closed tube yields water, and becomes black. C.c.: 43'5 silica, 43 5 magnesia, and 13 water; but with 1 to 8 iron protoxide, and also carbonic acid, bitumen, and chrome oxide.

Varieties are—(1) Noble Serpentine, brighter coloured, 16H 2 O, and more translucent; (2)' Picrolite, or fibrous (H. =3'5 to 4 '5); (3) Common, or compact; (4) Chrysotile (Baltimorite, ΛΓetaxite), in fine asbestiform fibres, easily separated, with a metallic or silky lustre (G. =2'219).

Common in Shetland, Urquhart, Portsoy, Ballantrae; Lizard Point in Cornwall; Norway, Sweden, North America. Chrysotile at Colafirth and Fetlar, Shetland, Portsoy, Towanreiff, in Scotland; Reichenstein in Silesia, the Vosges Mountains, and North America. Serpentine is often a product of decomposition, or pseudomorph of various minerals, as augite, hornblende, olivine, spinel, enstatite, garnet, &c. It forms whole rocks and mountains, and is manufactured into various ornamental articles.

550. Marmolite, 3MgSi + 2Mg0 2 .

Oblique prismatic; often foliated. H.=2'5 to 3; G. =2'41 to· 2'47. Lustre pearly. Greenish white, bluish white, and asparagusgreen. C.c.: silica 42'1, magnesia 38'5, water 17'5. In veins in serpentine of Urquhart and Portsoy (Scotland) Cornwall, Finland, Hoboken.

551. Antigorite.

Thin flat laminae. H. = 2 '5; G. — 2 '6. Translucent. Green with brown spots; streak white. C.c.: silica 40'8, magnesia 36'3, protoxide of iron 5'8, water 12'4. Antigorio in Piedmont.

552. Hydrophite, (Mg, i ’ e) 4 ¾ + 4Ö.

Massive and fibrous. H. =3 to 4; G. =2 ’ 65. Mountain-green to blue-black; streak paler. C.c.: silica 36 '2, magnesia 21Ί, protoxide of iron 227, water 16. Taberg in Sweden, New York.

553. Villarsite, 2Mg 2 Si + δ.

Right prismatic; crystals P, OP, meeting at 136°32', often twins in triple combination; also granular. H. =3; G. =2 ’ 9 to 3. Translucent. Greenish to greyish yellow. C.c.: silica 39 ’ 6, magnesia 47 ’ 4, protoxide of iron 3 , 6, water 5 ’ 8. Totaig, Ross-shire; Traversella, Piedmont; Forez, France.

554. Pyrallolite.

Oblique prismatic, C 72° 56'; columnar and granular. Cl. basic and hemidomatic, meeting at 94° 36'; fracture splintery; brittle. H. =3'5 to 4; G. —2'6. Translucent on edges; resinous. Greenish to yellow-grey. C.c.: silicate of magnesia and water. Storgard in Finland.

555. Dermatine, (Mg, Pe) Si+ 20.

Reniform; stalactitic; fracture conchoidal; brittle. H. — 2'5; G. =2 , 1. Resinous. Blackish green; streak yellow. Does not adhere to tongue. C.c.: silica 38, magnesia 22, protoxide of iron 12, water 23. Waldheim in Saxony.

556. Chlorophaeite, feSi + R 2 Si 3 + 4Ô.

Massive, rarely reniform. Coating or filling up geodes in amygdaloidal cavities. H. — 1 '5; G. = 2 Ό2 to 2 ’ 3. Sectile; fracture conchoidal. On first exposure transparent and olive-green to orangeyellow, but soon changes to black and opaque, splitting in so doing. Vitreous to shining. B.B. melts to a black glass. C.c.: silica 36 - 2, alumina 8'9, peroxide of iron 13 - 8, protoxide of iron 2 - 4, lime 3 ’ 8, magnesia 10, water 24 - 8. Rum and Canna in the Hebrides, Giant’s Causeway. The original mineral from Rum has 22 8 iron peroxide and no alumina.

557. Forchhammerite, FeSi + 6H.

Granular massive. Subresinous to dull. Dark green. H. =2: G. = l - 8. C.c.: silica 32 - 8, protoxide of iron 21 ’ 6, magnesia 3 - 4, water 42 2. Faroes.

558. Kirwanite.

Fills druses in amygdaloids with divergent sheaf-like crystals. H. =2; G.-2'9. Opaque. Olive-green to dark green. C.c.: silica 40 ’ 5, alumina 11'1, protoxide of iron 23'9, lime 19'8, water 4'4. Loch Baa in Mull; Mourne Mountains in Ireland.

559. Glauconite.

Round grains. Dull resinous. Light green. C.c.: silicate of protoxide of iron and potash. Ashgrove near Elgin; greensand of England, France, Germany, and America.

560. Celadonite, 3ÉSi 2 + R a Si 2 + 5H.

Massive, forming crusts, as of agates. Earthy, sectile. H. = 1 to 2; G. =2’6 to 2 ’ 8. Opaque, shining. Bright green. Feels creasy. C.c.: silica 54, alumina 3 ’ 8, ferric oxide 1Γ9, ferrous oxide 5 - 4, magnesia 6 - 8, potash 7’9, water 10. Orkney, Rum, and Fifeshire in Scotland. Giant’s Causeway, Verona, Faroes, Iceland, Cyprus, Bohemia.

561. Stilpnomelane, 2(Ëe, λig)Si + ÂÏSi + 2Ö.

Massive or radiating-foliated. One cl. perfect; brittle. H. = 3 to 4; G. = 3 to 3 ‘4. Opaque; vitreous to pearly. Greenish black. C. c.: 45’3 silica, 6 - 9 alumina, 38'3 iron protoxide (with 2 to 3 magnesia), and 9 ’ 5 water. Zuckmantel in Silesia and Weilburg in Nassau.

562. Chamoisite.

Oolitic and massive. H. =3; G. =3to 3 - 4. Greenish grey to black; streak paler. C.c.: silica 14 ’ 3, alumina 7'8, protoxide of iron 60’5, water 17'4. Chamoison (or Chamoson) in Valais, the Vosges. Berthierine has 75 protoxide of iron and 5 of water; Moselle.

Augite and Hornblende Group.

Hornblende and augite rather represent groups of mineral substances than single species. They are best distinguished when imperfectly formed, by the cleavage and angles of the prisms.

563. Enstatite {Chladnite), MgSi.

Right prismatic. o□P 92° to 93°; crystals ooPoo (a), oofao {b), °oP (wi), ⅛Poo (⅛), ⅜fao (j), ⅜P∞ (ψ), $P (τ) (fig. 497).

Usually imbedded, or indistinct granular masses. Cl. macrodiagonal very perfect, prismatic ooP distinct, brachydiagonal imperfect. H. = 5 - 5; G. =3’1 to 3'3. Translucent throughout, or only on the edges; vitreous or pearly on the more perfect cleavageplanes. Colourless, greyish or greenish white, yellowish, or brown. Not affected by acids. B.B. almost infusible.

C.c.: 60 silica and 40 magnesia, but with 6 to 8 iron protoxide, 1 t . 0 ? alumina, and 1 or 2 water. In olivine and serpentine rocks in Moravia, the Harz (Baste), and the Pyrenees.

564. Bronzite {Schiller Spar, Bastite), (Mg, f ’ e )⅛ι.

Right prismatic. ooP 94°; only granular and foliated. Cl. brachydiagonal perfect, prismatic less so; fracture uneven, splintery. H. =4 to 5; G. —3 to 3’5. Translucent on thin edges; metallic pearly. Green, inclining to yellow or brown. Imperf ec ∣ly sol. in h. acid, wholly in s. acid. B. B. becomes magnetic, and fuses in very thin splinters. C.c.: 43 silica, 26 magnesia, 27 lime,. 7’4 iron protoxide, 3’3 iron peroxide, 2 - 4 chrome oxide, 17 alumina, and 12 - 4 water. Bastite is possibly altered enstatite. Belhelvιe and Black Dog in Aberdeenshire, Baste, Tyrol, Baireuth, Styria. j

565. Paulite {Hypersthene), (Èe, Mg)Si.

Right prismatic. ooP {m) 93° 30', P2 {c), 2p2 {i), ⅜P⅜ {u), 00P2 {n), ⅛Poo (A), ooPαo {a), ∞Po θ {b), ⅜Pαo {k), 2P∞ {d). Granular or disseminated. Cl. brachydiagonal very perfect, prismatic ooP distinct, macrodiagonal very imperfect. H. = 6; G. = 3 ’ 3 to 3 - 4. Opaque or translucent on thin edges; vitreous or resinous, but metallic pearly on the cleavage planes, of which one is copper-coloured to violet or silvery. Pitch-black and greyish black; streak greenish grey or pinchbeck-brown, inclining to copper-red. Not affected by acids. B.B. melts more or less easily to a greenish black glass, often magnetic. C.c.: generally 46 to 58 silica, 0 to 4 alumina, 11 to 26 magnesia, 1 to 5 lime, 13 to 34 iron protoxide, 0 to 6 manganese protoxide. Portsoy and Craig Buroch in Banffshire, Barra Hill in Aberdeenshire, Paul’s Island, Labrador, and Greenland. Crystals occur in sanadine bombs at Lake Laach {Amblystegite), and in meteorites of Breitenbach. Hypersthene rock in Norway, Elfdal in Sweden, Cornwall (?), the Harz, and Canada. Chemically enstatite and paulite pass into one another; the essential difference is that the axial dispersion is uniformly p < v in the former, and the opposite in the latter.

566. Wollastonite ( Tabular Spar), CaSi.

Oblique prismatic, C 84° 30'. ooP 87° 18', 0P (u or h'), oop∞ (cor p), ooP⅜ {z) 110° 7', ooP c 2 {x or e ’) 51°, - Poo {v) 44°

27', ⅜Poo {a) 69° 56' (fig. 500). Rarely crystallized, mostly broad prismatic or laminar. Frequently fibrous. Cl. along 0P and ∞P 0 ∞ perfect, but planes uneven or rough; meet at 95° 23'. H. =45 to 5; G. =2'8 to 2'9. Translucent; vitreous or pearly on cleavage. White, inclining to grey, yellow, red, or brown; stι⅜k white.

Phosphoresces with heat or friction; gelatinizes in h. acid. B.B. difficultly fusible to a semitransparent glass. C.c.: 51'7 silica and 48'3 lime, but with 0 to 2 magnesia and 0 to 2 iron protoxide. Glen Gairn, Crathie, &c., in Aberdeenshire, Urquhart in Inverness, Skye, Banat, Finland, Sweden, Vesuvius (fig. 501), North America, Ceylon, Capo di Bove.

567. Augite (Pyroxene), fcSi = (0a, Mg, tfe)Si.

Oblique prismatic, C 74’11'. ooP87 0 6' 5 P (s: s) 120’48'; - P («) 131’ 30'; 2P (o) 95" 48'; OP; 3P; ooP 0 oo. In fig. 130 α>P (Jf), ooP 0 oo (r), ooP c ∞ (Z),P(s); also various twins and hemitropes of same form (figs. 191, 502, 503). Almost always prismatic, imbedded, or attached; also granular, columnar, and scaly. Cl. prismatic along α>P (with angles of 87° 6' and 92’ 54'), generally rather imperfect; orthodiagonal and clinodiagonal imperfect. H. =5 to 6; G. = 3 to 3 - 5. Pellucid in all degrees; vitreous; in some pearly on ooP 0 oo. Colourless, and white, but usually grey, green, or black. B. B. generally fusible; imperfectly soluble in acids. C.c. generally as follows :— [table]

Analysis gives 47 to 56 silica, 20 to 25 lime, 5 to 15 magnesia, 1 to 20 iron protoxide, with 0 to 3 manganese protoxide and 0 to 8 alumina. The alumina, chiefly found in very dark green or black augites, may in some replace either silica or part of the silicate.

The more important varieties are—

Diopside. —Greyish or greenish white, to pearl-grey or leek-green; streak white. Crystallized or broad columnar, or concentric lamellar. Transparent to translucent on the edges. Not affected by acids. B.B. fuses to a whitish semitransparent glass. C.c.: generally lime 26 and magnesia 18'5, with 55'5 silica. Mussa Alp (Mussite) and Ala (Aldlite) in Piedmont, Schwarzenstein in Tyrol, Scandinavia, Finland, Urals, and North America.

Malacolite, Sahlite.— White, green, rarely yellow, brown, or red; streak white. Translucent, or only on the edges; vitreous, inclining to pearly.

Seldom crystallized, mostly columnar or lamellar. B.B. melts to a darkcoloured glass. Malacolite common in primary limestones in Scotland, as at Shinness, Ledbeg (fig. 505), and Glen Tilt. Fassa Valley (Fassaite), Piedmont, Arendal, Philipstadt in

Sweden; Lake Baikal (Baikalite); near Lake Lherz in the Pyrenees (Lherzolite) ; Sala (or Sahla) in Sweden (Sahlite) ; Shinness (figs. 504, 506), Glenelg, Tiree, in Scotland; Tyrol; North America. Coccolite is a granular sahlite or augite.

Augite.— Leek-green, greenish black, or velvet-black, rarely brown; streak greenish grey. Vitreous to resinous; translucent or o,paque. Only slightly affected by acids. B.B. fuses to a black, often magnetic glass. An essential component of many rocks, as basalt, dolerite, clinkstone, and augite porphyry; Germany, Auvergne, Vesuvius; St Kilda, Rum, Tiree, Dalnain, and Urquhart in Scotland. Augite crystals in basalt often contain very many microscopic crystals and glasses; also pores with fluid carbonic acid.

Hudsonite.— Cleavable lamellar, and jet-black, with green streak and bronzy tarnish, from the Hudson river; the most highly ferruginous variety.

Amianthus.— Some asbestiform minerals are augite, but the greater number hornblende.

Breislackite.— Fine yellowish or brown woolly crystals. Vesuvius, and Capo di Bove near Rome.

568. Diallage, (Ca, Mg, f ’ e)Si.

Like augite, and only a variety with very perfect cleavage in the clinodiagonal, which forms with a second cleavage an angle of 87°. Lustre metallic pearly; colour grey or pinchbeck-brown. H. = 4; G. = 3 23. B. B. melts easily to a greyish or greenish enamel. C.c.: 50 to 53 silica, 1 to 5 alumina, 15 to 23 magnesia, 11 to 20 lime, and 5 to 20 manganese protoxide. Constituent of the augite rock of the Cuchullins in Skye and of the gabbro of Unst and Ayrshire. Baste in the Harz, Silesia, the Alps, Apennines, and Urals. Vanadine Bronzite, containing soda and vanadic acid, is similar. At Craig Buroch (Banffshire) diallage passes in paulite.

569. Jeffersonite.

Oblique prismatic. Cl. prismatic ooP 87° 30', and orthodiagonal. H. = 4 - 5; G. = 3 '3 to 3 '5. Dark olive-green, brown to black. Lustre greasy. A manganese and zinc augite, with 10‘2 protoxide of manganese, and 10 - 15 oxide of zinc. Sparta in New Jersey.

570. Acmite, 2FeS⅛+3RSi.

Oblique prismatic. Crystals long often acute-pointed prisms. ooP 87° 15', ooP<≈o (r), P(s), 6P (o), -6P ’ 3(z) (figs. 507, 508). Cl. like augite. H. =6 to 6’5; G. =34 to 3 ’ 6. Nearly opaque; vitreous. Brownish or greenish black; streak greenish grey. Imperfectly soluble in acids. B.B. fuses easily to a black magnetic glass. C. c.: 52 silica, 30 iron peroxide, 5 iron protoxide, and 13 soda, but with 1 to 3 manganese peroxide, and also 3 to 4 titanic acid. Eger and Porsgrund in Norway.

571. Aegérine, R 2 Si 6 + RSi

+ 2NaSL

Oblique prismatic; striated or reed-like prisms of 86’ 30' to 87’ 45'. Cl. orthodiagonal perfect, less distinct clinodiagonal, and prismatic. H. = 5 ’5 to 6; G. =3 ’ 4 to 3’5 or 3’6. Vitreous; translucent on edges, or opaque. Greenish black. B.B. fuses easily, colouring the flame yellow. Scarcely affected by acids. C.c.: 49 silica, 31 ’ 7 iron peroxide, 6'6 iron (and manganese) protoxide, and 12 ’ 7 soda, with a little magnesia and potash. Has the same relation to augite as arfvedsonite to hornblende. Near Brevig and Barkevig in Norway.

572. Spodumene, 4AlSi 8 + 3(Li, Sa, ⅛)Si.

Oblique prismatic, C 69’40'. ooP87°(fig. 509). Cl. prismatic o>P and orthodiagonal, perfect; chiefly massive or foliated. H. =6 - 5 to 7; G. = 3 ’ 1 to 3‘2. Translucent; vitreous or pearly. Pale greenish grey or white to applegreen; streak white. B.B. intumesces slightly, tinging the flame momentarily purplish red, and fuses easily to a colourless glass. Not affected by acids. C.c.: 65 silica, 28 ’ 7 alumina, and 6 - 3 lithia. Killiney near Dublin, Utö in Sweden, Tyrol. Killinite (sp. 651), from Killiney, seems to be decomposed spodumene.

573. Petalite (Castor), 4AlSi β + 3(Li, Na)S⅛.

Oblique prismatic. Castor has C 67’ 34' and ooP 86° 20', in irregular rectangular prisms, petalite being massive and coarse granular. CL basal, distinct; in a second direction (meeting at l∙41⅜ 0 ) less so. H. =6’5; G.—2’4 to 2'5. Greenish, greyish, or reddish white to pale red. Translucent; vitreous or pearly. B. B. melts easily into a porous obscure glass, colouring the flame red. Not affected by acids. C.c.: 78’3 silica, 17"4 alumina, 3’2 lithia, and 1’1 soda. Utö, Bolton in Massachusetts, York in Canada. Castor in Elba. Milarite, valley of Milar, Switzerland.

574. Rhodonite {Manganese-Spar}, MnSi.

Anorthic, oof 00(a); ooP≡o (5); OP (c); ooP'(u); f'oo (i); Poo(s); 'Poo (o); nι'P'oo {t). a: b lll 0 9'; e: a 93° 28'; n: a 106° 19'; but chiefly massive or granular. Cl. oo Poo and OP, meeting at 87° 38', perfect; brittle. H.-5 to 5 5; G. =3’5 to 37. Translucent; vitreous or partly pearly. Dark rose-red, bluish red, or reddish brown. Not affected by acids. B. B. fusible. C.c.: 45 - 8 silica and 54’2 manganese protoxide, with 3 to 5 lime and 0 to 6 iron protoxide. St Marcel, Lângban, Ekaterinburg, the Harz, and New Jersey. Bustamite, pale greenish or reddish grey, with 14 lime, Mexico; Fowlerite, New Jersey, with 7 to 11 iron protoxide; and Paisbergite, Sweden, are varieties. Hydropite, Photicite, Allagite, and Horn·Manganese are mere mixtures.

575. Babingtonite, 9(Ca, Fe, Mn)Si + ⅛eSi s .

Anorthic. Crystals very low eight-sided prisms, small, attached. g : h 90° 24'; c: a 87° 27'; a: b 112° 12'; b: d 81° 8'; c: d 150° 10' (fig. 511). Cl. basal (c), very perfect; also along b. H. =»5’5 to 6; G. =3’3 to 3 - 4. Thin laminae translucent. Splendent vitreous; black. Not affected by acids. B. B. fuses easily with effervescence to a black magnetic bead. C. c.: 50 7 silica, 11 iron peroxide, 10 ’ 3 iron protoxide, 7'7 manganese protoxide, and 20 - 3 lime, in the Arendal specimens; one from Nassau gave about 17 of peroxide, with protoxides only 11. Tongue (Sutherland), Portsoy (Banffshire), Arendal, Nassau, and Gouverneur (New York).

576. Szaboite, HFeSi 3 + 2CaSi.

Anorthic. ooP'(Z); oo'P (m) 88° 40'; ooPoo (5); ooP<≈o (a); P'(p);

'P (o); 2'P,a> tø); 2P'oo (®) (fig. 512). H. = 6’5; G. = 3 , 5. Brownish red to reddish yellow. Pleochroic. C.c.: silica 52’4, peroxide of iron 447, lime 3 1. Slightly sol. in s. acid, more so in h. acid. Calvario on Etna, Mont Dore.

577. Anthophyllite, 3MgSi + PeSi.

Right prismatic. ooP 124° 30'. Cl. macrodiagonal, perfect. Clove-brown to purplish brown and leek-green. Translucent; radiating and foliated. Pearly on cl. plane. H. = 5‘5; G. =3’2. C.c.: silica 55'9, protoxide of iron 167, magnesia 27’8. B.B. very difficultly fusible. Hillswick, Shetland; Kongsberg and Modum, Norway; Greenland, and the United States.

578. Hornblende.

Oblique prismatic (figs. 513 to 517; see also fig. 192). Distinct cleavage in several directions. H. — 4 to 6, but generally 5 (will scratch with knife); G.-2 ’ 5to 4'0, but mostly high. Mostly coloured. Lustre vitreous, in some silky or metallic pearly. Sol., but not very readily, in acids; more or less easily fusible. C.c.: anhydrous silicates and aluminates of lime, magnesia, iron protoxide; more sparingly of soda, yttria, and manganese protoxide. The chief species form by their decomposition highly fertile soils.

Amphibole.— Oblique prismatic, C 75° 10'. ∞P 124° 30', P 148° 30'. The crystals short and thick, or long and thin prismatic; formed especially by ooP (m), ooP c 00 (χ), and bounded on the ends chiefly by 0P (p) and P (r). Twins common, with the chief axis the twin axis. Yery often radiated, fibrous, or columnar, or granular Cl. prismatic along ooP 124⅛ o , very perfect; orthodiagonal and clinodiagonal very imperfect. H. = 5 to 6; G. =2 , 9 to 3'4. Pellucid in all degrees; vitreous, but sometimes pearly or silky. Colourless or white, but usually some shade of grey, yellow, green, brown, or black. B. B. fuses, generally intumescing and boiling, to a grey, green, or black glass. Those containing most iron are most fusible, and are also partially sol. in h. acid, which scarcely affects the others. C.c. very variable; the silica is partly replaced by alumina, specially in the green or black varieties; RO is chiefly MgO, CaO, and FeO. Lime is the most constant element, in most from 10 to 12; magnesia and iron protoxide replace each other, the one increasing as the other diminishes. With 4Si and R = 2Mg + lCa + lie, the average compositionis 53 ’ 6 silica, 17 ’ 8 magnesia, 12’5 lime, and 16 Ί iron protoxide; but analyses give 40 to 60 silica, 0 to 17 alumina, 0 to 30 magnesia, 10 to 15 lime, 0 to 36 iron protoxide (or peroxide), and 0 to 4 manganese protoxide, 0 to 8 soda, 0 to 3 potash, and 0 to Γ5 fluorine with a little water.

The more important varieties are—

Amianthus, Asbestos, and Byssolite, 2MgSi + CaSi. Fine fibrous. White, grey, or green. The fibres often easily separable, elastic, and flexible. Unst, Shinness, Portsoy, Savoy, Tyrol, Corsica.

Tremolite, Grammatite, 3MgSi + CaSi, with 58’35 silica, 28’39 magnesia, and 13’26 lime. White, grey, green; in long prismatic crystals, often striated longitudinally. Pearly or silky; semitransparent or translucent. B. B. fuses readily to a white or nearly colourless glass. Loch Shin (Sutherland), Glen Tilt, Glenelg, Tiree, Cornwall, Cumberland, Sweden, the Alps, Pyrenees, Silesia, Siberia, North America.

Nephrite, or Jade, is a tough, compact, fine-grained tremolite, with H. =6 to 6’5; G. =2’9 to 3’1. Fracture close splintery. Very tenacious. Translucent; dull to resinous. Leek-green to blackish green. Feels slightly greasy. Formerly made into ring-stones, amulets, idols, and war axes. New Zealand, China, Mexico, Peru, Balta (Shetland).

Actinolite, Actinote, or Strahlstein (Ca, Mg, Fe) Si. Colour green, inclining to black, grey, or brown. Translucent throughout, or only on the edges. Long prismatic crystals, or radiated-columnar masses. B. B. melts to a greenish or blackish enamel. Fethaland and Colafirth and Hillswick (Shetland), Oronsay, Ord Ban (Inverness), Sweden, Tyrol, North America.

Hornblende.— 6RSi + R 2 Si 3 ∙ Green or black, seldomer brown or grey. G. =31 to 3’3. *B.B. fuses rather easily to a yellow, greenish, or black enamel. Three varieties are distinguished, (a) The noble or Pargasite, pale celadon-or olive-green, and strong pearly or vitreous lustre; at Pargas in Finland, Tyrie in Scotland. {b} Common hornblende, dark leek-or blackish-green, opaque; streak greenish grey. A constituent of many rocks, as in Norway, the Alps, and Scottish Highlands (Ballater, Ben Arihaar, Glen-bucket, Colafirth), (c) Basaltic, foliated, with bright even cleavage, opaque, velvet-black; streak grey or brown. Generally contains alumina (9 to 15) and much (5 to 11) iron peroxide. In e basalt and volcanic rocks. Etna, Vesuviu⅝ Rhineland, Bohemia.

579. Arfvedsonite, RSi + FeSi 3 .

Oblique prismatic. ooP; ooP c αo; P; 2P c ∞ 120° 24'; OP. Cl. ∞P 124° 22', perfect; also OP. Massive. Black; opaque. Vitreous. H. =6; G. =3’44. C.c.: silica 43, alumina 4'5, peroxide of iron 3 - 8, protoxide 34, lime 5'7, soda 8’5. Streak dark blue-grey. Fusible in fine splinters in the flame of a candle. B.B. intumesces and melts easily to a black magnetic globule. Not sol. in acids. Kangerdluarsuk in Greenland, Frederiksvärn, Arendal, El Paso in Colorado.

580. Pilolite, 4MgSi 2 + AlSi 2 + 150 .

Felted or matted fibres more or less dense. Cream yellow to buff. Dull; extremely tough; absorbs water like a sponge. H. = 1 to 2’5; G. = ’ 68 to 1 ’ 34. Structure varies considerably, and has given rise to trivial names, as mountain paper, mountain leather, mountain flesh, rock cork, &c. Mountain Paper occurs in thin sheets at Boyne Castle near Banff; Mountain Leather, Burn of the Cairn (Cabrach), Tod Head (Kincardineshire), Leadhills, Strontian; Rock Cork, Portsoy and Boyne Castle, Saxony, and Sweden. C.c.: silica 51’6, alumina 8 ’ 6, ferrous oxide 2’88, magnesia 10’2, water 23’3.

581. Krokidolite, 3FeSi + (Na,Mg)Si s + 2H.

Delicate, easily separable, but tough fibres; elastic. H. = 4; G. = 3 - 2 to 3 ’ 3. Translucent; silky. Indigo-blue; streak lavender. B.B. fuses easily to a black magnetic glass. C.c.: silica 50’3, iron protoxide 35, magnesia 2’2, soda 6’7, water 5’8. Stavern in Norway, Greenland. A fibrous yellow mineral from Orange river, South Africa, has been referred here; its fibres are not separable, and its hardness is 7. Abriachanite, a very similar mineral, of blue colour, occurs near Inverness.

582. Glaucophane, 9RSi + 2AlSi 3 .

Oblique prismatic. Cl. prismatic, perfect; fracture conchoidal. H. — 5’5; G. =3’1. Translucent; vitreous to pearly. Indigoblue, grey, bluish black. B. B. becomes brown, fusing easily to olive-green glass. C.c.: silica 56’5, alumina 12’2, protoxide of iron 10 ’ 9, magnesia 8, soda 9 ’3. Island of Syra.

583. Hermannite, MnSi.

Granular and arborescent. Rose-red. G. =3’4. C.c.: protoxide of manganese 46’7, silica 48’9, lime 2, magnesia 2’4. Cummington in Massachusetts.

584. Grunerite, FeSi.

Asbestiform. G. =3’7. Brown; silky lustre. C.c.: protoxide of iron 51 ’55, silica 45 ’45. Mt. des Maures (Var).

585. IθLiTE {Cordierite, Hichroite), A 2 Si 3 + 2(Mg, i , e)Si.

Right prismatic. ∞P (P) 119° 10', middle edge of P 95° 36'. Form ooP (7 7 ), ooPoo (Z), OP (m); and this with ∞P∞ (⅛), ooP3 {d), P∞ (π), and ⅜P (s), (fig, 518); short, prismatic. Cl. ∞Poo distinct, traces along Poo; fracture conchoidal or uneven. H.=7 to 7’5; G.=2’5 to 2’7. Transparent or translucent; vitreous, inclining to resinous. Colourless, but chiefly dark blue, or violet, green, brown, yellow, and grey. Often with distinct trichroism; on OP blue, on ooPoo grey, and on α>Poo yellowish. B.B. fuses difficultly to a clear glass; slightly affected by acids. C. c.: 48 to 51 silica, 29 to 33 alumina, 8 to 13 magnesia, 1 to 12 iron protoxide. Cabo de Gata in Spain, Bodenmais {Peliom y ), Orijerfvi in Finland {Steinheilite'), Norway, Sweden, Greenland, North America, and Siberia. Small rolled masses of an intense blue colour and transparent, found in Ceylon, are the Sapphire d’Eau or Luchssapphir of the jewellers.

The following have been considered cordierite altered, or with 2 to 6 atoms water :—(a) Bonsdorfite, Hydrous Polite, greenish brown or dark olive-green; near Abo. (ά) Esmarkite, Chlorophyllite, large prisms or foliated, green or brownish; near Cabrach (Aberdeen), Brβvig in Norway, Unity in Maine, and Haddam in Connecticut, (c) Fahlunite, Triclasite, compact, greenish brown or black, foliated; H. =2’5 to 3; G. — 2’5 to 2’8; Falun, {d) Huronite, granular; pearly, yellowish-green; H —3’3; G.-286; infusible and insoluble; Lake Huron, (e) Weissite, kidney-shaped and ash-grey or brown; Falun and Lower Canada. (∕) Pyrargillite, indistinct imbedded crystals, black passing into brown or red, dull resinous lustre; H. — 3’5; G. =25; Helsingfors, (g) Pinite, crystallized, or massive and laminar, with imperfect cleavage; H. = 2 to 3; G. — 2’7 to 2’9, semitranslucent or opaque, dull or resinous, and dirty grey, green, or brown; B.B. fuses to a glass, sometimes clear, at other times dark-coloured; Auvergne, Schneeberg, Penig in Saxony, the Harz, Cornwall, Cabrach and Torry (Aberdeenshire), the United States, and Greenland {Gieseckite, sp. 650). Oosite from Geroldsau in Baden, snow-white, opaque, fragile, is similar, {h) Gigantolite ; H. =3’5; G. =28 to 2’9; opaque, dull resinous, and greenish grey or brown; B. B. intumesces slightly, and fuses easily to a greenish slag; Tammela in Finland. (i) Praseolite, lamellar and green; Brevig in Norway.

586. Emerald {Beryι), ⅛lSi 3 + 3GlSi.

Hexagonal; P59° 53'. Crystals of α>P, OP, and ooP, ooP2, OP, P (a, p, c, s, fig. 519) are prismatic, generally with vertical striae. Cl. basal, rather perfect; ooP imperfect. H.=7∙5 to 8; G.=2 , 6 to 2’8. Transparent or translucent; vitreous. Colourless or white, but generally green, sometimes very brilliant; also yellow and smalt-blue. B. B. melts with difficulty on the edges to an obscure vesicular glass. Not affected by acids. C.c.: 67’5 silica, 18’7 alumina, and 13’8 glucina, with 0’3 to 3 iron peroxide, and 0’3 to 3’5 chrome oxide in the rich green emerald. Emerald, bright green; G. =2’710 to 2’759; occurs in Muso Valley near Bogota, also in Salzburg and the Urals. Beryl, or Aquamarine, colourless, or less brilliant; G. =2’677 to 2’725; near Mursinsk and Nertchinsk in Siberia, Salzburg, and Brazil; in the United States, where at Grafton, between the Connecticut and Merrimack, crystals 4 to 6 feet long, and weighing 2000 to 3000 tb, occur; Mourne Mountains in Ireland; Mount Battock and Cairngorm in Scotland (fig. 98). Common Beryl at Falun in Sweden, Fossum in Norway, Limoges in France, Rabenstein in Bavaria, Nigg Bay and Pitfodels and Rubislaw near Aberdeen {Daυidsonite}, Struay Bridge (Ross). Emerald and beryl are much valued as precious stones. Known from quartz by face p. Forms shown in figs. 92, 95, 96, 97, 98, 276.

587. Leucophane, 6CaSi + 3Gl⅛i + 2NaF.

Right prismatic. ooP 91°. Cl. basal perfect. H.=3 ’ 5 to 4; G. =2’97. Pellucid. Wine-yellow to olive-green. Vitreous. B.B. fuses to pale violet-blue bead. C.c.: silica 47, lime 23’4, glucina 10’7, soda 11’3, fluorine 6’6. Lamo in Norway.

588. Melinophane, 7(ħ 3 Si 2 ) + 6NaF.

Pyramidal. P 122° 23'. Mostly lamellar. H. =5; G. = 3. Honey-yellow to citron-yellow. Brevig and Frederiksvärn.

Felspar Group.

Crystallization oblique prismatic or anorthic; very similar both in aspect and in angles. Cl. very distinct, especially the basal P; less so the clino-or brachydiagonal Μ. G. =2’4 to 3’2, but mostly 2’5 to 2’8; H. = 6 or a little more. Slightly or not at all soluble in acids. B. B. fusible, but often with difficulty. Translucent; pure varieties transparent. Colourless, white, or shades of red; less commonly of green or yellow. C.c.: anhydrous silicates of alumina, and of an alkali or alkaline earth.

The felspars are very important constituents of the earth’s crust, occurring in nearly all the igneous rocks, and in many of the stratified crystalline schists. In true strata they are found chiefly as fragments or decomposed, and in the latter state form a large part of wet soils and clays. By the older mineralogists and in popular language many species are conjoined under the common name of felspar which are now considered as distinct, each of them having not only its peculiar physical and chemical characters, but also geognostic position and associated groups of minerals. Thus orthoclase, and the other more siliceous felspars with potash, abound in granite and the plutonic rocks; the less siliceous, with soda and lime, characterize the volcanic rocks,— e.g., labradorite the basaltic group, glassy felspar the trachytic. Orthoclase is associated with quartz, hornblende, and mica; glassy felspar either with hornblende and a black mica or with augite; labradorite with augite, very rarely with quartz or hornblende.

The felspars are best known from similar minerals by their hardness (they scarce scratch with a good knife), difficult fusibility, and unequal cleavages. The following marks may aid 'the student in distinguishing the more common species. In orthoclase the basal cleavage plane forms a right angle with the clinodiagonal cleavage planes Μ on both hands; in the triclinic or plagioclase felspars the angles are unequal. Orthoclase, albite, andesine, and oligoclase are insoluble in acids; labradorite and anorthite are more or less soluble. In granite, when decomposing, orthoclase often becomes reddish or dark-red; oligoclase dull green, and at length white.

Waiterhausen considers that the felspars are mixtures of three true species, forming a series with the oxygen of the silica, alumina, and RO in the proportions x : 3 :1,— x ranging from 24 to 4. Tcher-mak and most mineralogists now take a similar view, regarding orthoclase, albite, and anorthite alone as true species, of which the others are mixtures. Those consisting essentially of potash and soda only are mechanical mixtures of orthoclase and albite, the distinct lamellae being visible by the microscope; those again that contain essentially lime and soda together are, sometimes at least, chemical, being isomorphous compounds of albite and anorthite in various proportions, and with corresponding transitions in crystallographic and physical properties. Notwithstanding this, these intermediates must be regarded as independent mineral species, inasmuch as they are severally typical of certain rocks, and have characteristic forms differing from each other in angular inclination.

589. Orthoclase, AlSi i + KSi 3 .

Oblique prismatic, C = 63° 57 z . ∞P {T and Z) 118° 47'; P o ∞ (x) 65’ 46'; 2P c oo (n) 90’71'; 2P°∞ (y) 35° 45'. The commonest and simplest forms are ooP, OP, P<>oo , and o□P c oo (3f), ooP, OP (P), 2P 0 oo (figs. 520 to 527). When ooP predominates the crystals are short rhombic prisms; when coP c oo predominates they are tabular; when ooP and α>P c oo predominate they are short hexagonal prismatic, when OP and ooP 0 oo they are rectangular prismatic, often much lengthened. Twins are very frequent, and occur according primarily to four laws. First, through revolution of one half or of a whole crystal, then forming interpenetrating twins round a vertical axis (fig. 195). In the case of this hemitropic revolution one of the external faces becomes a face of union. According as the right or the left half (or whole crystal) is conceived to be that which has been revolved the crystals are termed right and left, as in figs. 188, 189. Second, by revolution of one half around an axis normal to M∙, in such twins the composition is not evidenced externally except by sutures. Third, through revolution round an axis normal to P, forming orthorhombic prisms which show a herring-bone lineation, through the meeting of striae commonly present upon the face Μ parallel to the intersection of its edge with the face T (fig. 528). Fourth, by revolution round an axis normal to 2P c ∞ (n); this also forms a prism the section of which is nearly square (fig. 529). Compound twins on this last type are formed of 3 to 4 end 8 crystals (fig. 530).

Occurs also massive, and coarse or fine granular. Cl. basal (P), very perfect; clinodiagonal (3f), perfect (P: Jf = 90°); fracture conchoidal or splintery H. = 6; G. =2'53 to 2’58. Transparent to translucent on the edges; vitreous but pearly on cl.; and also opalescent, with bluish or changing colours. Occasionally colourless but generally red, yellow, grey, or green. B. B. fuses with difficulty to an opaque vesicular glass. Not affected by acids. C.c.: 64 ’ 6 silica, 18 ’ 5 alumina, and 16 - 9 potash, but generally 10 to 14 potash, 1 to 4 soda, 0 to l - 3 lime, 0 to 2 iron peroxide. Varieties are—

(1) Adularia and Ice-spar, transparent or translucent, splendent, and almost colourless. Some with bluish opalescence are named Moonstone ; St Gotthard, Mont Blanc, Dauphiné, Arendal, Greenland, and Ceylon.

(2) Common Felspar, generally white or red, especially flesh-red, is a common constituent of many rocks. Crystals at Baveno on Lago Maggiore, Lomnitz in Silesia, Mourne Mountains and Wicklow in Ireland, Aberdeenshire (at Rubislaw 6 or 8 inches long) in Scotland, and at Carlsbad and Elnbogen in Bohemia. Amazon Stone, verdigris-green, from Sutherland, Lake Ilmen, and Colorado, and Murchisonite, golden or greyish yellow, from Arran and Dawlish, are varieties.

(3) The Glassy Felspar or Sanidine (C 64° 1', ot>P 119° 16') contains 3 to 12 potash and 3 to 10 soda. Crystals imbedded; vitreous, translucent, and often much cracked; Arran, Eigg, and other parts of Scotland, Drachenfels, Auvergne, and other countries.

Orthoclase occurs in granite, gneiss, and porphyry in many countries. It is commonly associated with quartz; sometimes, as in the Graphic Granite of Sutherland, Harris, and Portsoy, in letter-like combinations of the latter. It is very liable to decomposition, when it is converted especially into kaolin, used for manufacturing porcelain and stoneware. The adularia or moonstone and the green amazon stone are cut as ornamental stones. Leelite, from Biddean nam Bian in Argyllshire and Grythyttan in Sweden, is a somewhat siliceous horny-lustred flesh-coloured compact variety. Petuntze and Hornstone are similar but more impure. Microcline is a variety with angle distorted by interstitial penetration, by oligoclase (Sutherland), and by albite (Frederiksvärn, &c.).

590. Albite, AlSi 3 + NaSi 3 .

Anorthic. OP (P): ooι><≈ (Μ) 86° 24'; ooP' (Z): oo'P (?) 122’ 15'; but angles variable. Crystals, generally like those of orthoclase, are tabular or prismatic (fig. 197). Hemitropes common, especially united by a face of α>foo (figs. 531, 532) the re-entering angle between the faces of 0P (Pand P ’) 172’ 48' being very cl; ractcristic. Fig. 198 is another common hemitrope. Also massive, an I in radiating plates. Cl. basal and brachydiagonal, almost equally p∙∙∙ , c t; fracture conchoidal or uneven. H. =6 to 6*5; G. =2 J > 2∖∙7. Rarely transparent; vitreous, pearly on the cl. Colom, i.ss, 1 t generally white, grey, green, red, or yellow; streak white. B. 11. difficultly fusible, tinging the flame yellow, to a white semiopaque glass.

Not affected by acids. C.c.: 68‘6 silica, 19 ’ 6alumina with 01 to 1 iron peroxide, and 11 - 8 soda, with 0‘3 to 4 lime, 0 to 2 ’ 5 potash. Hence albite and orthoclase both contain soda and potash, only in different proportions. Albite is most easily recognized by its frequent re-entering angles, its readier fusibility, and the obliquity (93’ 36') of its cl. planes, often marked with striae. Pericline is a variety of which fig. 533 is a typical form.

Albite is a constituent of many “greenstones,” as at Corstorphine (Edinburgh), and of granite, syenite, gneiss, porphyry, and trachyte. Crystallized at Murdoch’s Cairn, Aberdeenshire, being the colourless felspar of the red granites of Scotland. Dauphiné, St Gotthard, Tyrol, Salzburg, and Arendal.

Adinole is a compact variety similar in appearance to Leelite. 591. Anorthite, AlSi + CaSi.

Anorthic. 0P (P): oofoo (Μ) 85’ 50'; α>P , (Z): oo'P(7) 120’ 30'. Hemitropes common on both Μ and P. Anglβbetween P and P 180’ 24'. Cl. basal and brachydiagonal, perfect. H. — 6; G. = 2'7to2 ’ 78. Transparent or translucent; vitreous. Colourlessor white. B. B. fuses to a clear glass; soluble without gelatinizing in con. h. acid. C.c.: 43 silica, 36'9 alumina, 20 Ί lime, sometimes with magnesia and soda. Fetlar in Shetland; Lendalfoot in Ayrshire, in gabbro; Monte Somma, Iceland, Java. Lepol·ite and^4wι- phodelite are varieties. In Latrobite the greater part of the lime is replaced by potash. Glen Gairn and Labrador. At both rose-red.

592. Oligoclase, 2AlSi 3 + (Na, Ca) 2 Si 3 .

Anorthic. OP: α>P∞ 86° 10'; ooP': oo'P 120° 42'. Hemitropes face m, with p: p , 173° 4'; I: I 120° 20'; y : y 179° 9'; x: x 175° 59'. Cl. basal, perfect; brachydiagonal, less so. H. =6; G. =2‘62 to 2‘84. Vitreous, resinous on the cl. White, with a tinge of green, grey, or red. B.B. melts easier than orthoclase or albite to a clear glass; not affected by acids. C.c.: 63 silica, 23'4 alumina, 8 , 4 soda, and 4 - 2 lime; thus nearly = 3 albite and 1 anorthite. Distinguished from orthoclase by the marked striae on the faces; less readily from albite, but more fusible and G. higher. The common associate of orthoclase in the Scotch grey granites, especially in vein granite, as at Rispond and Ben Loyal (figs. 536, 537) in Sutherland, and at

Rubislaw; Scandinavia, Urals, Harz, and North America. The Sunstone, from Foinaven in Sutherland, Norway, Lake Baikal, and Ceylon, with a play of colour due to imbedded crystals of rubinglimmer (göthite), belongs to this species.

593. Labradorite, AlSi 3 + (Ca, Na)Si.

Anorthic. OP: α>foo 86° 40'; OP: α>'P lll 0 ; OP: ∞P' 113° 34'; ooP': oo'P 121° 37'; oof∞: ooP' 120° 53'; ooPo 0 : oo'P 117° 30'. Hemitropes of three types :—(1) according to the first law of orthoclase as in fig. 538; that is, vertical revolution and face of union <z>Poo; (2) revolution of one half with reunion on the face α>P∞, as in fig. 539; (3) with twin face P, as in fig. 540. Hemitropes of the last form also occur in which the lower half consists of a hemitrope formed according to the second method. Crystals imbedded in rocks consist generally of repeated twins affording an angle of 173° 20'. Cl. basal, perfect; brachydiagonal, less so; both usually striated on account of the above twinning. H. = 6; G. = 2 '68 to 2 74*. Translucent; vitreous, on the cl. resinous. Grey, passing into white, green, yellow, or red. The faces of ooPoo often exhibit very beautiful changing colours—blue, green, yellow, red, or brown—sometimes bands intersecting at certain angles. B. B. fuses more readily than orthoclase to a compact colourless glass. Sol. in h. acid. C. c.: 52 - 9 silica, 30'3 alumina, 12'3 lime, and 4’5 soda. It is thus = 1 albite and 3 anorthite. Common constituent of dolerite, gabbro, and hypersthene rocks. In Scotland, Labrador, Finland, Harz, Tyrol; also at Etna and Vesuvius.

594. Andesine, AlSi 3 + (NaCa)Si.

Anorthic. Crystals similar to albite and anorthite. Twin face Μ. Crystals generally formed of repeated plates. G. = 2 '67 to 2'7. Physical properties like albite; more easily fusible to a porous white glass; h. acid sometimes dissolves out alternate laminae of crystals. C. c.: 59'7 silica, 25 - 6 alumina, 7 '7 soda, and 7 lime, and thus nearly 1 of albite and 1 anorthite. Typical of the primary limestones and a granitic belt therein in Scotland, as at Shinness, Urquhart, Dalnain, &c. In the Andes, the Vosges, and Iceland.

595. Hyalophane, AlSi 3 , KSi 8 + AlSi, BaSi.

Oblique prismatic; resembles orthoclase; crystals and angles nearly the same. Cl. 0P, perfect. H. =6 to 6'5; G. =2‘8 to 2 - 9. Transparent. Lustre vitreous. Colourless, white, and flesh-red. C.c.: silica 52'7, alumina 21, baryta 15'1, potash 7’8, soda 2'1. B.B. difficultly fusible to a blebby glass, not acted upon by acids. Binnen in Valais, Jacobsberg in Sweden.

596. Barsovite, AlSi + CaSi.

Right prismatic, or oblique prismatic. H. =5'5 to 6; G. =2'58. Snow-white; translucent. Fracture granular. Pearly. C.c.: silica 42'2, alumina 36'4, lime 19 - 8. Gelatinizes in h. acid, difficultly fusible. A dimorphic form of anorthite. Barsovskoi in the Urals.

597. Saussurite.

A massive, granular, translucent, white or pale green felspathic mineral of the nature of anorthite mixed with labradorite. H. = 6 to 7; G. = 3 '26 to 3 '4. Probably a mixture. Occurs in loose blocks near Geneva, and in Corsica. In China and in India is carved under the name of Oriental jade (nephrite). Seems to be confounded also with zoizite, and perhaps with yu (prehnite). Jadeite is similar.

Zeolite Group.

These crystallize in all the systems except the anorthic, and themselves present great variety of development. Mostly hyaline and white; rarely red, grey, or yellow. Cl. generally distinct. All yield water in closed tube; all fusible B. B. most easily, and often intumescing; all sol. in acids, and mostly gelatinize or deposit silica. They are hydrated silicates of alkalies, or alkaline earths, mostly with silicates of alumina, but rarely contain magnesia. Some mineralogists regard the water as basic, in union with silica, and Kenngott gives the formula in that form, thus :—

Analcime, (fta’Äl) 2Si + 2(ft, Si),

Natrolite, (NaAl) 2Si + 2(ft,Si),

Stilbite, Ca, 'A1÷6(0, Si), and the others similar. They are generally found in amygdaloidal cavities or fissures of trap or plutonic rocks, apparently as deposits from water percolating into them, and are thus probably products of decomposing nepheline or felspars, or hydrated felspars themselves. They never form constituents of roçks. Natrolite, scolezite, thomsonite, and the connected varieties are marked by their needle-like radiating forms; stilbite and heulandite by their broad, foliated, pearly cleavage.

598. Pectolite, 4CaSi + ⅛iaSi 2 + ft .

Oblique prismatic, C 84° 37'. ooP∞ (c); 0P (ω) 95° 23'. Cl. c and u. Twin-face c; chiefly spheroidal and radiating fibrous. H. = 5;

G. =2'74 to 2'88. Translucent; crystals pearly; fibres silky. Pale green to yellowish white. Sol. in h. acid, leaving silica. C.c.: 54'2 silica, 33'7 lime, 9'4 soda, and 2'7 water. Ratho, Corstorphine, Castle Rock, and Arthurs Seat, Edinburgh; Kilsyth, Stirling; Knockdolian and Lendalfoot, Ayrshire; Skye; Montebaldo; Monzoni Valley in Tyrol.

599. Walkerite, 4CaSi + MgSi + NaSi 2 + 2H.

Like pectolite, but columnar. H. = 4 '5; G. — 2 '7. Flesh-coloured. Lustre pearly to greasy. C.c.: silica 53'7, lime 28'6, magnesia 5'1, soda 7'9, water 4'6. Corstorphine Hill, Burntisland.

600. Xonotlite, 4CaSi + ft.

Massive. H. - 6; G. - 2 '6 to 2 '7. Pink, white, and grey. Tough; fracture conchoidal and splintery. C.c.: silica 49'8, lime 43'5, protoxide of manganese 2'3, protoxide of iron 2'9, water 3 ’ 7. Kilfinichen and Torosay (Mull), Xonotla (Mexico).

601. Tobermorite, 3(Ca 4 , 0)Si 6 + 2J0.

Massive, fine granular; translucent; fracture hackly. H. — 5; G. — 2 - 4. Pale pink. C.c.: silica 49'8, lime 37'2, water 12'9. Tobermory (Mull), Dunvegan (Skye).

602. Okenite, CaftSi 3 + H.

Right prismatic. «P 122° 19'. Usually fine fibrous; radiating. H. — 5; G. =2'28 to 2'36. Pellucid; slightly pearly. Yellowish to bluish white. In powder easily sol. in h. acid, leaving gelatinous flakes after ignition. C.c.: 56'6 silica, 28’4 lime, and 17 water; an apophyllite without the fluorine. Disco Island, Faroes, and Iceland.

603. Apophyllite, 8(0aSi + 2⅛) + KF.

Pyramidal. P 120° 56'. P, ∞Poo (m), OP (o), o□P2 (r). Rarely lamellar. Cl. o, perfect. Brittle. H. — 4'5 to 5; G. ∙=2 - 3 to 3'4. Transparent; vitreous. On o pearly {lchthyoph-thalmite). Colourless, rarely pink, green, red, brown, and yellow. B.B. exfoliates, intumesces, and melts to white enamel. Sol. in h. acid, leaving silica. C.c.: silica 50'3, lime 24'7, water 15'9, potassium 4'3, fluorine 2Ί. Dunvegan and Storr, Skye (fig. 544); Chapel, Fife; Corstorphine (fig. 542) and Ratho, near Edinburgh; Kilsyth, Bowling, Kilpatrick; Port Rush, Ireland. In the form P (fig. 79), grass-green at Oxhaveer, Iceland (Oxhaυeerite) ; Utö, Sweden; Audreasberg and Faroes (pink); Faroes, and Poonah in India (green). Internal structure tesselated, being built up of wedge and lenticular forms with varying refractive indices, hence exhibiting a beautiful structure with polarized light.

604. Gyrolite, (⅜Ca + ⅜0)Si + H.

Lamellar, radiate, spherical, and investing. H. — 3 to 4. Pearly. Bluish white to cream-coloured. Transparent, rapidly becoming opaque. C.c.: silica 53'3, lime 32'9, water 13'8. Quiraing, Lyndale, and Storr, Skye; Loch Screden and Carsaig, Mull; Canna; Karartut, Niakornak, and Disco; Faroes; Nova Scotia.

605. Analcime, AlSi 3 + NaSi + 2Ö.

Cubic, ooθoo; 202. Fracture uneven. H. — 5 '5; G. — 2 Ί to 2 '28. Colourless, white, flesh-red, scarlet. Vitreous; transparent. B.B. melts without frothing to a clear vesicular glass. Decomposable with gelatinization in h. acid. C.c.: 54'5 silica, 23'3 alumina, 14Ί soda, 8'2 water. Walls, Orkney; Talisker, Skye; Sanda, and Hebrides generally. Transparent at Eigg, and Elie, Fife scarlet at Bowdens, Kincardine; opaque white at Glen Farg, Salisbury Crags, and Dumbarton;

Giant’s Causeway, Seisser Alp in

Tyrol, Cyclopean Islands (fig. 545), Faroes, Iceland, and Nova Scotia. Eudnophite is a variety. Pectolite (sp. 598) occurs pseudomorphous after analcime, in large crystals of α, n, at Ratho, Edinburghshire.

606. Pollux, 3(AlSi 8 +(⅛⅛, Na⅜)Si) + 2Ö.

Cubic, ooθoo; 202 (fig. 546). Also massive. Gum-like externally. Brittle, with traces of cleavage. Fracture conchoidal. H. ≈5'5 to 6'5; G. = 2 - 86to 2 ’ 9. Colourless. Vitreous. Sol. in n. acid. C.c.: silica 44, alumina 16, oxide of caesium 34, soda 2'5, water 2'4. Elba. The only mineral which contains caesium in quantity.

607. Faujasite, 2A1S⅛ + (Cal⅛a) 2 Si 8 +18⅛.

Cubic; in octahedrons with the icositetrahedron ∣O∣. Fracture uneven; brittle. H. — 7; G. —1'92. Transparent; vitreous to adamantine. White to brown. Sol. in h. acid. C.c.: 46 8 silica 16 alumina, 4'4 lime, 4'8 soda, 28 water. Kaiserstuhl in Baden’ Annerod near Giessen, Eisenach, Marburg.

608. Chabasite {Lime-ChdbasiU∖ AlSi 3 + CaSi + 6H .

Rhombohedral; R 94 β 46. ' ⅛⅜R⅛; - ⅜R (r); - 2R (e); ooP2 (a). Twins very common (generally intersesting), on faces ooP and

Poo. Primary rhombohedron is sometimes twinned with a crystal with faces r, e, s. Cl. r perfect. H.-4 to 4'5; G.-2 to 2'2. Transparent or translucent; vitreous. Colourless, and brownish, yellowish, brick-, and flesh-red. Sol. in h. acid, leaving silica. C.c.: silica 47'8, alumina 20'8, lime 10'7, water 21'3. Lyndale (figs. 547, 548, 549), Talisker (figs. 176, 550, sometimes flesh colour), and Storr, Skye (figs. 547, 548); Port Glasgow and Kilmalcolm (pink and brown); Giant’s Causeway and Magee Island (red), Faroes, Iceland, Aussig, Andreasberg (fig. 551). Haydenitc in twinned rhombohedra, with p: p 95° to 97° and p: d 170° reentering (fig. 552), from Fassa and Maryland, is similar.

Phacolite is chabasite in twins of ∣P2, α>P2, R, - ⅜R at the Giant’s Causeway (fig. 154). At Richmond in Victoria they occur as in fig. τ

553, - 2R (π), - ∣R (r), ⅜P2 (0, 0P (c); polar edge, ∣P2 145 . In this, half of the lime is replaced by soda.

609. Gmelinite {Soda-Chdbasite), AlSi 3 + NaSi + 6H .

Hexagonal. R 112° 26'; P 79° 54'. CombinationJ ’, 0P, <*>P (figs. 554, 556). Faces of P striated parallel to the polar edge, those of the prism horizontally (fig. 555). Cl. α>P distinct. Gelatinizes with h. acid. C.c.: 47'6 silica, 19'7 alumina, 12 soda, 20’7 water. Certain crystals seem to indicate twinning. Talisker in Skye (twins of fig. 555), Glenarm in Antrim (fig. 555), Vicenza, Pyrgo in Cyprus, Cape Blomidon in Nova Scotia.

610. Levyne, AlSi 2 + CaSi +

05.

Rhomboh; R (s) 79° 29 ’; - ⅛R (r) 1 ’ ° 3'; OR (o). Forms intersecting twins as in fig. 557. H. =4; G. =2 ’ 1 to 2'2. Colourless and white. C.c.: silica 43 - 8, alumina 23 ’ 8, lime 9'7, water 21. Storr in Skye (o, s), Ireland (at Glenarm, Island Magee, Londonderry, &c.), Iceland, Dalsnypen and Naalsö in the Faroes.

611. Herschelite, AlSi 3 +

(CaNa)Si + 5H.

Hexagonal prisms (e) surmounted by two trihedral pyramids of α 7 and one of α 1 √(fig. 558). α 7 : e 122° 8'; α⅛-: e 107° 26'; « striated horizontally. Cl. e; fracture conchoidal; transparent; vitreous. White or colourless. H. = 5 ‘5; G. =2'06. C.c.: silica 47, alumina 21 ’ 2, lime 5'2, soda 4'8, potash 2, water 17'86. Aci-Castello and Palagonia in Sicily, Yarra in Australia.

612. Laumontite {Leonhardite}, AlSi 3 + CaSi + 4H.

Oblique prismatic, C 80° 42'. ooP (m) 86° 16'. ooP: - coP (β) 113° 30'; P∞ (a⅛)ια>P 111° 14'; e: a 125° 41'; a: b 90°; e: z 149° 15'. Twin face a. Cl. m, perfect; very brittle. H. = 3 to 3'5; G. = 2'2 to 2'3. Pellucid when fresh; vitreous; pearly on cl. White, cream-coloured, brick-red. Decomposes rapidly through loss of water. B. B. intumesces, and melts first to a white enamel, ultimately to a clear glass. Gelatinizes in h. acid. C.c: silica 50’9, alumina 21'8, lime 11'9, water 16'3. Rapidly loses 1 equivalent or 3'86 per cent, of water, and becomes friable (Hypostilbite). Kilfinichen, Mull (ng. 559); Storr and Quiraing, Skye (hypostilbite); Tod Head, Snizort, Glen Farg (red); Bowling, Dumbarton (twins of m, e) ; Huelgoat in Brittany; Prague, Falun, Iceland, Faroes, Nova Scotia. Caporcianite from Tuscany has only 3 water.

613. Epistilbite {Reissite),

AlSi 3 + CaSi 3 + 5H.

Oblique prismatic, C 54° 53'. ooP (m) 135° 10'; Poo (i) 109° 46'; ⅜P(s)147°40'(fig. 560). Hemitropes united by m, with twins of the same united by the brachydiagonal (a). Cl. brachydiagonal, perfect. H. = 3 '5 to 4; G. — 2 '3 to 2 ’ 4. Pellucid; vitreous; pearly on cl. Colourless. Sol. without gelatinizing. C.c.: silica 59, alumina 17'5, lime 9, soda 1'5, water 14'5. Talisker in Skye (τn, t, a); Hartlepool (in twins), Iceland, Faroes, Silesia, Viesch in Valais, Nova Scotia, and New Jersey.

614. Heulandite, AlSi s + CaSi 3 + 5ÊE.

Oblique prismatic, C 63° 40'. P o ∞ (p) 50° 20'; 2P (z); f P («);

2P c ∞ (r); 3Pcoo (s); α>Poo; ooP c ; 0P. z: z 136° 4'; u: u 146° 52'. Crystals elongated along each of the axes present very varying forms, but generally tabular Cl. clinodiagonal, perfect; pearly on this, vitreous on others; brittle. H. =3'5 to 4; G. =2'1 to 2'2. Transparent to translucent; colourless, white, brick-red, rose, green, hairbrown. B. B. melts with exfoliation and intumescence to a white enamel. Sol. in h. acid, leaving silica. Storr and Talisker, Skye (fig. 562); Sanda; Kilmalcolm; Catterline, Kincardine (fig. 563); Kilpatrick Hills {p, m, n, z, u, r, s) and Kintyre (red); Iceland, Faroes, Fassa Valley, Nova Scotia, Baltimore (Beaumontite) (fig. 565) (p, m, n, z, t) ; Vindhya Mountains in India (fig. 564).

615. Brewsterite, AlSi 3 + R⅛i 3 + 5H. R = (∣Sr + ∣Ba + ∣Ca).

Oblique prismatic, C 86° 56'. ooP 0 ∞ (a); ∞P c ∞ (δ); OP (o); nP c ∞ (e); ∞P (τη); ooP<≈2 (c); ∞P c ⅜ (i). e·.e 173° 10' (fig. 566). Cl. clinodiagonal, perfect; pearly on do., vitreous on others; pellucid.

H. =5 to 5'5; G. =2 ’ 5 to 2'45. Colourless, yellow, or brown. Sol. with gelatinization in h. acid. C.c.: 54'3 silica, 15 alumina, 9 strontia, 6'6 baryta, 1'3 lime, 13'5 water. Strontian, Freiburg in the Breisgau, Pyrenees.

616. Phillipsite, AlSi 3 + (Ca, ½)Si + 5H.

Oblique prismatic, C 55° 1'. ∞P (τn); ooP c ∞ (5); 0P (c). Polar edges 120° 42' and 119° 18'. Faces b and m striated parallel to the intersections. Apparently always twinned; generally these duplicated by intersection on face b or face c (figs. 567, 568), and frequently arranged so that three of the above double twins intersect at right angles to one another, forming the cruciform fig. 569.

When the prismatic faces of these are short, the faces m of the intersecting individuals fall nearly into one plane, presenting the form fig. 570; when long, fig. 190. Brittle; fracture uneven. H. =4’5; G. =2’15 to 2’2. Gelatinizes in h. acid. C.c.: silica 48'6, alumina 20 ’ 2, lime 7'3, potash 6‘2, water 177. Giant’s Causeway, Giessen, Marburg, Cassel, Capo di Bove, Vesuvius, Iceland.

617. Harmotome, AlSi 3 + BaSi 2 + 50.

Oblique prismatic, C 55° 10'. ∞P (s); ∞P ∞ {b) ; OP (α)∙ Forms like phillipsite, but more frequently in simple twins. Physical properties like phillipsite, but G. — 23 to 2’5, and fuses with difficulty. Difficultly sol. in h. acid. C.c.: 46’5 silica, 15’9 alumina, 23'7 baryta, and 13’9 water. Strontian, transparent {Morvenite, fig. 572) and opaque (figs. 571, 573); Glen Arbuck (fig. 574) and Bowling in Dumbarton; Corstorphine near Edinburgh; Andreasberg, Kongsberg, Oberstein.

618. Stilbite, AlSi 8 + CaSi 3 + 6Ö.

Oblique prismatic, but with right prismatic habit; C 50° 49'∙ oo Poo (a); oopoo(Z>); P (r); ooP2 {m) ; OP (p). Cl. a, perfect. H. =3’5 to 4; G. ≡2Ι to 2’2. Transparent; vitreous. Pearly on a. Colourless, white, yellow, pale brown, brick-red. Decomposed by h. acid, leaving silica. C.c.: silica 57’5, alumina 16 ’ 4, lime 8’9 water 17’2. Storr and Talisker in Skye (a, b, p> (fig. 575), and in Hebrides (colourless); Arran and Kilmalcolm (pale brown); Long Craig (Dumbarton) and Kinneff (Kincardine) (brick-red); Iceland, Faroes, Andreasberg, Vindhya Mountains, Wellington Mountains (Australia), Nova Scotia.

619. Pufflerite, AlSi 3 + Ca 2 Si 3 + 5Ö.

Fibrous globular concretions, with vitreous surface. H. =4; G. —2’21. Greyish white. Transparent. C.c.: silica 52 - 8, alumina 16’3, lime 1Γ2, water 17’2. Pufflatsch in the Seisser Alp.

620. Edingtonite, 4AlSi 2 + 3BaSi + 12H.

Pyramidal; hemihedral with inclined faces. P 87’ 19'; ⅜P (n) 129° 8'; ooP (a); polar edges P 92° 51' (fig. 576). Cl. a, perfect; fracture uneven. H. = 4 to 4’5; G. —2 7 to 271. Translucent; vitreous. Colourless.

C.c.: silica 37'3, alumina 2375, baryta 26’52, water 12’46. Kilpatrick Hills in Dumbartonshire.

621. Foresite, 2⅛lSi a + (i⅛a, Ca 3 )Si 2 + 6H.

Right prismatic. α>Poo; ooPoo; OP. Cl. brachydiagonal, perfect; lustre thereon pearly. G. =2 ’ 4. White. C.c.: silica 50, alumina 27‘4, liπ!e 5'5, soda 1’4, water 15’1. San Piero in Elba.

622. Natrolite, AlSi 2 + NaSi + 2H.

Right prismatic. ooP (m) 91’; P (o); polar edges 148° 20' and 144 β 40', middle edge 53° 20'; ooPoo (⅛); ooP<x> (a). Radiating acicular crystals, often fibrous. Cl. ooP, perfect. H. =5 to 5’5; G. =2’17 to 2’26. Pellucid; vitreous. Colourless, ochre-yellow, reddish. Is not pyro-electric. B.B. melts quietly to a clear glass, colouring flame yellow. Sol. in oxalic acid. C.c.: 47’2 silica.

27 alumina, 16’3 soda, 9’4 water. Glen Farg (fig. 577), (colourless and reddish), Tantallon Castle (fig. 578), Dumbarton, Bowling (green), Campsie, Bishopton, Glenarm and Port Rush (Ireland), Auvergne, Hesse, Hohentwiel in Swabia, Norway. Crocalite is red, fibrous, and investing; Kintyre, Forfarshire, Wemyss Bay. and the Urals.

623. Scolecite, AlSi 2 + CaSi + 3H .

Oblique prismatic, C 89’ 6'. α>P (m) 91 β 35'; P (o) 144’ 20; - P. Prismatic and acicular crystals. Twins common, on face α>P c ∞, one face with feathered striae. Cl. ∞P, perfect. H. =5 to 5’5; G. =2’2 to 2’3. Pellucid; vitreous; pyro-electric. White to reddish white. B.B. twists in a vermicular manner; melting readily to a porous glass. Only partially sol. in oxalic acid. C. c.: silica 45’8, alumina 26’2, lime 14 - 3, water 137. Staffa; Loch Screden, Mull; Talisker, Skye; Berufiord, Iceland (fig. 579); Faroes; Vindhyas, India.

Natrolite and scolecite pass into one another. There are two definite intermediates— Fargite, consisting of two equivalents of natrolite and one of scolecite, and Mesolite, consisting of one of the former and two of the latter. The first of these occurs at Glen Farg and at Bishopton {Galactite) ; the second is the ordinary radiated zeolite of the amygdaloids of the Tertiary igneous rocks of the Hebrides and the Faroes. It there occurs in matted crystals of extreme tenuity {Cottonstone), also in delicate feathery tufts; in Renfrewshire in spheres with an internally radiated structure, and also in needle form and in downy tufts.

624. Gismondine, AlSi + (5aSi + 4H.

Pyramidal. P (δ) 92° 30'; polar angle 118° 34'; ooPα> (fig.

580). Cl. P. H.-5, on edges and angles 5 to 6; G. — 2 ’ 26. Translucent; vitreous. Bluish white to pale red. C.c.; silica 35’9, alumina 27’3, lime 13Ί, potash 2’8, water 21Ί. Island Magee and Larne, Ireland; Vesuvius, Aci-Castello, and Capo di Bove; Schiffenberg near Giessen; Schlauroth near Görlitz.

625. Zeagonite, AlSi + (CaK)

Si + 4H.

Right prismatic. P polar angle 120° 37' and 121° 44'; middle angle 89° 13'. Crystals like fig. 419. H. ≈5, on edges and angles 7; G. — 2 - 2. Transparent; vitreous. Colourless, white, or bluish. C.c.: silica 44, alumina 23 - 3, lime 5’3, potash 11Ί, water 15’3. Capo di Bove.

626. Thomsonite, 2AlSi + 2(CaNa)Si + 5H.

Right prismatic. α>P (nt) 90’ 26'; oopoo (a); oopoo (b) ; ⅛Poo (y); P∞ (r); ≠ β Pa> (x). x: x 177° 34' 20". Cl. macrodiagonal and brachydiagonal, both perfect. H. —5 to 5’5; G. =2’35 to 2’38. Translucent; vitreous; pearly on macrodiagonal. Colourless. B. B. difficultly fusible with intumescence to a white enamel. Sol. with gelatinization in h. acid. C.c.: silica 38 7, alumina 30’8, lime 13 - 4, soda 4’4, water 131. Lochwinnoch, Renfrew; Kilpatrick (fig. 58° ' i · Quiraing and Talisk< (sometimes massive-granular); Rathlin and Magee Island, Ireland; Faroes, Vesuvius (fig. 581), Sicily, Bohemia, Tyrol, Nova Scotia.

Faroelite is a variety with 42 ’ 5 of silica. It replaces thomsonite generally in Tertiary igneous rocks, occurring at Storr and elsewhere in the Hebrides, Faroes, Iceland, and Nova Scotia. The angle of the vertical prism is within 8' of that of thomsonite. It contains an equivalent more silica.

627. Prehnite, AlSi + 20aSi + Ö.

Right prismatic. ooP (nι) 99° 58'; OP (c); 3Poo (e)33° 26'j JPo θ (v)90°32'; ∞Poo (a); oopoo (J); P (s). Crystals either tabular of c, or prismatic along both the vertical and the brachydiagonal axes, hence varying much in form. Also in fan-shaped and botryoidal aggregations. Cl. c, perfect; pearly thereon, vitreous elsewhere. H. = 6 to 7; G. =2 ’ 8 to 3.

Transparent to translucent. Colourless, but generally green of bright but pale tints, also lemon-yellow. Becomes electrically polar by heat. B.B. intumesces greatly, melting to a porous enamel. Decomposed by h. acid. C.c.: silica 43 - 6, alumina 24 ’ 9, lime 27 ’ 1, water 4‘4. Glen Gairn, Aberdeen (fig. 583); Skye and Mull; Corstorphine Hill (green and pink), Castle Rock (white), and Salisbury Crags (yellow), Edinburgh; Frisky Hall, Dumbartonshire (fig. 584); Hartfield Moss, Renfrew (botryoidal); Cornwall; Dauphine; Tyrol: Cape of Good Hope; China (Yu).

628. Friedelite, Mn 4 Si 3 + 2H.

Rhombohedral; R 123° 42'. OR; ooR. Tabular habit, and in granular aggregates. Cl. basal,perfect. H. =4 to 5; G. =3 1. Rose-red, with paler streak. C. c.: silica 36, protoxide of manganese 53, lime 2 - 96, water 7 ’ 9. Adervielle on the Neste de Louron (Pyrenees).

Hydrous Silicates of Alumina.

These are probably for the most part products of decomposition of felspars under atmospheric exposure.

629. Kaolin (Porcelain Earth), ^lSi 2 + 2H.

Massive; in beds and veins. Fracture uneven; fine earthy, very soft, sectile, and friable. H. = 1; G. = 2 - 2. Opaque, dull. White or grey, inclining to blue, green, yellow, or red. Feels meagre, not greasy when dry, and plastic when wet. B.B. infusible. Not affected by h. acid, but decomposed by warm s. acid, leaving silica. C.c. very variable, but approximates to 46 silica, 40 alumina, and 14 water. Chiefly a product of the decomposition of orthoclase, or of granite, porphyry, and other rocks containing that mineral. Cornwall and Devonshire in England are the chief European localities for the kaolin used in manufacturing porcelain.

Clays are merely varieties of kaolin, mixed with quartz-sand, carbonate of lime, magnesia, and the oxyhydrates of iron. Often 40 to 50 silica, 30 alumina, 13 to 20 water, and 4 iron peroxide, with lime and potash. In the fire they are infusible, burning hard. Generally they are compact and friable, of white, yellow, red, blue, grey, or brown colours. Their specific gravity varies from 1 ’ 8 to 2 - 7. The following are varieties. Pipe-clay, greyish or yellowish white, with a greasy feel, adheres strongly to the tongue, when wet is very plastic and tenacious, and in the fire burns white. Abundant in Devonshire, and in the Trough of Poole in Dorsetshire; in France, Be⅛ium, and Germany. Used for manufacturing tobacco-pipes and similar articles. Potter's Clay, red, yellow, green, or blue, becoming yellow or red when burnt; more easily fused than the former, and often effervesces with acids. That used in the potteries in England comes chiefly from Devonshire. Loam, coarser and more impure, with more sand, and consequently less plastic. Shale or Slate Clay, greyish black, and much mixed with bituminous or carbonaceous matter. Bituminous Shale, known by its shining resinous streak. Black Chalk, with more carbon, leaves a black mark on paper. Iron Clay contains much peroxide of iron, is reddish-brown, and forms the basis of many amygdaloids and porphyries.

630. Nacrite, AlSi 2 + 20.

Right prismatic; minute six-sided tables in fan-like group; and scaly. H. = 0 , 5 to 1; G. = 2 ’ 35 to 2 ’ 6. Glimmering to pearly, snow-white or yellowish white. C.c.: silica 46’3, alumina 39’8, water 13 - 9. A crystalline form of kaolin. Fins in Allier, Mons, Freiberg, Pennsylvania, and coal formation commonly.

631. Lithomarge.

Kaolinic substances, compact, earthy, and pseudomorphous. H. = 2 ‘5 to 3; G. — 2 ∙4 to 2 - 6. White, yellow, or red. Greasy, adheres to tongue. Klausthal, Harz, &c. Similar are Carnat, Myelin, Melopsite.

632. Halloysite, AlSi + 4H.

Massive and reniform. H. = l - 5 to 2’5; G. —1 , 9 to 2 ’ 1. Translucent when moist. Bluish white, green, or yellow. C.c.: 41 - 5 silica, 34 ‘4 alumina, 241 water. Hospital Quarry near Elgin, on the Tweed, Liege, Tarnowitz, Eifel (Lenzinite). Fuller’s Earth may be an impure ferruginous variety. Maxton in Scotland, Reigate and Maidstone in England, Saxony, Bohemia, &c.

633. Glagerite, Al 2 Si 3 + 6H.

H. =1; G. =2 - 35. Bergnersreuth. Malthazite, from Steindörfel near Bautzen, has less alumina.

634. Kollyrite, Al s Si + 9H.

H. =1 to 2; G. — 2. Also similar. Schemnitz, Pyrenees, and Saxony. Scarbroite from Scarborough has 10H 2 O.

635. Miloschin.

Conchoidal or earthy. H. =2; G. — 2 1. Indigo-blue to celadongreen; has 2 to 4 chrome oxide. Rudnik in Servia.

636. Montmorillonite, Al 2 Si 7 + 2H.

Massive. Rose-red. Montmorillon and elsewhere in France, Poduruoj in Transylvania.

637. Razoumoffskin, AlSi 3 + 3H.

From Carinthia. Chrome Ochre, with 2 to 10 per cent, of chrome oxide, from Waldenburg in Silesia and Creusot in France, is similar.

638. Cimolite, ⅛l 2 Si β + 6H.

Pseudomorphous after augite. Bilin, Limburg, Kaiserstuhl, Argentiera and Milo.

639. Allophane, AlSi + 5H.

Botryoidal and reniform. Fracture conchoidal; brittle. H. =3; G. = 1 , 8 to 2. Pellucid; vitreous. Pale blue, white, green, or brown. Colour due to copper. Charlton, Woolwich, Baden, and Bonn.

640. Pyrophyllite, AlSi 4 + H .

Right prismatic, but radiated, foliated. Cl. perfect; flexible, sectile. H. =1; G. =2 - 8 to 2 ’ 9. Translucent, pearly. Light verdigris-green to yellowish white. B. B. swells up with many twistings to a white infusible mass. C.c.: 67 silica, 28 alumina, and 5 water. Urals, Spa, Morbihan, Westana in Sweden, Carolina, and Brazil. Tdlcosite, from Heathcote in Victoria, has silica and alumina about equal.

641. Anauxite, AlSi 4 + 3H.

Granular. H. =2 to 3; G. =2 - 2 to 2 - 4. Translucent, pearly. Greenish white. C.c.: 60 , 5 silica, 26 alumina, and 13’5 water. Bilin in Bohemia.

Hydrous Silicates of Zirconia, Thoria, &c.

642. Malacone, 3ZrSi + H.

Pyramidal. P 83° 30'. Typical form ooPα>, P, ooP. H. — 6; G. = 3∙9to4 , l. Conchoidal fracture. Lustre vitreous. C.c. same as zircon, but with 3 of water in the Hitterö variety and over 9 in that from Finland. Has a surface opalescence, and may be altered zircon. Hitterö, Chanteloube (near Limoges), near Dresden, Rosen-dal, Finland, Miask.

643. Eucrasite.

Right prismatic (?). H. =4 ’ 5 to 5; G. =4’39. Lustre greasy. Blackish brown; streak brown. Translucent on edges. Fracture uneven; brittle. C.c. very complex: silica 16, thoria 36, cerium protoxide 5’5, peroxide 6, lanthania 2 ’ 4, yttria 4’3, erbia 1’6, titanic acid 1 ’ 3, ferric oxide 4 ’25, alumina 1 ⅛, water 9. Barkevig near Brevig.

644. Thorite, ThSi + 2Ö.

Pyramidal. ∞P: P 133° 30'. Generally massive. H. = 45 to 5. G. =5to5 - 4. Lustre brilliant vitreous; when weathered resinous. Fracture conchoidal when fresh, splintery when weathered. Brownish black to clove-brown. C.c. complex, but essentially 18 silica, 73 thoria, 9 water. In syenite at Lochan Hacon, and in a boulder on Ben Bhreck in Sutherland, in crystals (fig. 585); Löwö near Brevig, Norway. Uranothorite, from Arendal, has 50 per cent, thoria and 10 uranous oxide; found also at Hitterö and at Champlain (U. S.)

645. Orangite, 3ThSi + 2H.

Massive. Orange-yellow to cinnamon-red. Other characters like thorite. C.c.: 17 silica, 75 thoria, 7 water. Ben Bhreck, Langesund near Brevig. The mineral from Beu Bhreck passes gradually into thorite, which thus would appear to be altered orangite.

646. Tritomite, ⅛ 2 Si 3 + 4H.

Cubic. In tetrahedra. H. = 5'5; G. — 3 9 to 4'66. Lustre vitreous. Dull brown; streak yellowish grey. Subtranslucent. C.c. complex: silica 21, alumina 2 - 5, ceria 40, lanthania 15, yttria 4'6, lime 4, water 8. Lamö near Brevig.

Magnesian Silicates.

647. Agalmatolite (Figure Stone), 4AlSi 2 + KSi 3 + 3H.

Massive or slaty. Fracture splintery, rather sectile. H. =2to 3; G. = 2'8 to 2'9. Translucent; glimmering. Green, grey, red, and yellow. Feels somewhat greasy, but does not adhere to the tongue. Sol. in s. acid. C.c.: 55 silica, 33 alumina, 7'6 potash, and 5 water; but in many localities magnesian. Calligaig in Sutherland; China, where it is cut into various works of art; also Nagyag in Hungary, and Saxony.

648. Oncosin, 2AlSi 2 + (K,Mg)Si 2 + 20.

Fracture uneven or splintery; sectile. H. =2;G. — 2'8. Translucent; slightly resinous. Apple-green or brown. Sol. ins. notin h. acid. Salzburg.

649. Liebenerite.

Hexagonal. ooP; OP. Cl. prismatic, perfect; fracture hackly. H. —3’5; G. =2'8. Oil-green, bluish green, and greenish grey. Greasy lustre. C.c.: silica 447, alumina 36 ’ 5, potash 9'9, water 5 - 5. Monte Viesena near Forno, Predazzo in Tyrol.

650. Gieseckite.

Hexagonal. ooP; OP. Fracture splintery. H. =3 to 3’5; G. =27 to 2'9. Kangerdluarsuk in Greenland, Diana in New York.

651. Killinite, 2AlSi 2 + RSL 2 + 3H.

Crystalline, foliated. Cl. along a prism of 135’ 44'. G. =2'65. Greenish grey, yellow, or brownish green. C.c.: 48 silica, 31 alumina, 2 ’3 protoxide of iron, 6'5 potash, 10 water. Killiney near Dublin.

652. Hygrophilite.

Scaly. H. =2 to 2’5; G. =27. Greenish grey. Lustre and feel greasy. C.c.: silica 48'4, alumina 32 ’ 1, protoxide of iron 3 ’ 3, potash 57, water 9. Sol in h. acid. Halle on the Saale.

653. Bravaisite, R 2 Si 3 + 2AlSi 3 + 4H.

Aggregates of thin nlates. H. — 1 to 2; G. —2'6. C.c.: silica 51'4, alumina 18'9, peroxide of iron 4, magnesia 3'3, potash 6‘5, water 13'3. Noyant in Allier.

654. Pinitoid.

Massive. Leek-and oil-green. H. =2'5; G. =2'8. C.c.: silica 48'5, alumina 28, protoxide of iron 8, potash 5‘8, water 4 ’ 5. Freiberg and Chemnitz in Saxony.

655. Bole.

Earthy, in nests and veins. Conchoidal. H. = 1 to 2; G. = 2 , 2 to 2'5. Opaque; dull resinous; streak shining. Brown, yellow, or red. Feels greasy; some adhere strongly to the tongue, others not at all. In water crackles and falls to pieces. C. c. hydrous silicates of alumina and iron peroxide, in vanous proportions. Scotland, Ireland, Dransfeld, Clermont in Auvergne. Stolpenite, Rock Soap, Plinthite, Yellow Earth or Felinite, Fetbol, and Ochran are varieties.

656. Carpholite, ÂlSi + MnSi + 2Ö.

Right prismatic. P 11Γ 27'. Radiating stellated. H. = 5 to 5 '5; G. =2 - 9. Translucent; silky; straw-to wax-yellow. B.B. intumesces and fuses to an opaque brown glass. C.c.: silica 38, alumina 29 4, protoxide of iron 2'9, peroxide of iron 4, protoxide of manganese ∏'8, water 10'8. Schl⅛ggenwald, Wippra in the Harz, Meuville in the Ardennes.

657. Nontronite, ⅛⅛Si 3 + 50.

Massive; fracture uneven. H. =2 to 3; G. = 2 to 2'3. Opaque; dull or glimmering; streak resinous. Straw-yellow or siskin-green. B.B. decrepitates, becomes black and magnetic, but without fusing; sol. and gelatinizes in warm acids. C.c.: 43 silica, 36 iron peroxide, and 21 water, with 3'5 alumina and 2 magnesia. Nontron in France, Harz, and Bavaria. Chloropal is similar. B.B. brown. Unghvar in Hungary, and Passau.

658. Pinguite.

Massive; fracture splintery; sectile. H. — 1; G. — 2'3. Light to dark green. Lustre vitreous. Feels greasy. C.c.: silica 36 - 9, peroxide of iron 29'5, protoxide of iron 6'1, water 25 ’ 1. Wolkenstein, Suhl.

659. Hisingerite, Fe 2 Si 3 + 2i ’ eSi + 9H.

Reniform, and in crusts. H. —3'5 to 4; G. =2'6 to 3. Opaque, resinous. Brownish or bluish black; streak liver-brown or yellowish brown. C.c.: various, but 32 ‘5 silica, 33'5 iron peroxide, 15*1 iron protoxide, and 19 water, in the Thraulite from Bodenmais. Also Gilling and Riddarhyttan in Sweden, and Breitenbrunn (Polyhydrite).

660. Bergholz.

Fine fibrous; glimmering lustre. Wood-brown to green. G. — 2'4. C.c.: silica 55'5, peroxide of iron 19 ’ 5, magnesia 15, water 10 ’ 3. Sterzing in Tyrol. Xylite, probably from the Urals, is similar.

661. Umber.

Massive; fracture conchoidal. H. - Γ5; G. — 2'2. Liver-brown; streak shining. Mixtures of peroxide of iron, oxide of manganese, and alumina with water. Cyprus. Eypoxanthite and Siderosili∙ cite are similar.

662. Klipsteinite, (R 3 , R 3 ) 2 Si 8 + R 3 H 3 .

Compact. H. = 5 to 5’5; G. — 3'5. Liver-brown to black; streak yellow-brown. C.c.: silica 25, peroxide of iron 4, sesquioxide of manganese 57, water 9. Klappernd in Dalecarlia, Herborn near Dillenburg.

663. Wolkonskoite.

Amorphous. Horny; bluish green to grass-green. Fracture conchoidal; brittle. C.c.: silica 36, alumina 3, sesquioxide of chromium 19, ferric oxide 10, water 21. Okhansk in Siberia.

664. Rgttisite, 3NiSi + 4H.

Amorphous and reniform. Apple-green to emerald-green. H. =2 to 2’5; G.≈2'35 to2 ’ 37. C.c.: silica 437, nickel oxide 35'9, water 11 ·2. Röttis near Reichenbach in Saxony. Komarit is similar.

665. Uranophane, 3CaSi + U s Si 3 +18H.

Right prismatic. ooP 146°; α>poo; Poo; with polar angle 90°. Crystals honey-yellow; when massive leek-green. H. — 2'5; G.— 2 - 6 to 2 7 8. C.c.: silica 17, alumina 6*1, oxide of uranium 53 7 3, lime 5'1, water 15Ί. Kupferberg in Silesia.

666. Uranotile, 0aSi + U 3 Si 2 + 9H.

Right prismatic. ooP 164. In stellate groups. Lemon-yellow. G. = 3'96. C.c.: silica 13'8, oxide of uranium 6675, lime 5'27, water 12'67. Wölsendorf in Bavaria, Joachimsthal, Mitchel county in North Carolina.

667. Bismutoγerrite, Bi, Si 2 ,+ 2Fe,Si.

Crypto-crystalline; oblique prismatic. Siskin-to olive-green. H. = 3'5; G. = 4 '48. C.c.: silica 24, oxide of bismuth 42'8, peroxide of iron 33'1. Schneeberg in Saxony. Hypochlorite is a variety containing 13 of bismuth. In a third variety, from Bräunsdorf, antimony replaces bismuth.

Silicates with Titanates, Niobates, &c.

668. Sphene, CaSi 2 + CaTi 2 .

Oblique prismatic, C 85° 22 ’. ∞P (I) 133° 2',∙ ⅛P o αo(χ) 55 β 21'; P o ∞ (y)34° 21'; ∞P c oo tø): OP (Pore) 90°; ooP c 3 (Μ) 76° 7'; P c oo (r) 113’ 30'; ⅜P c 2 (n) 136° 12'; 4P c 4 (s) 67’ 57'. Crystals vary extremely in form, being generally apparently oblique-tabular, from predominance of n, which are hemidomes in alternate position on opposite ends; also, but more rarely, prismatic, with dominance of I and Λf. Twins frequent. Twin face c, and formed by revolution either (a) on an axis normal to c or (δ) on a vertical axis; the former very common and usually producing thin tables with a re-entering angle along one side, and sometimes elongated. Occasionally in double twins. Sometimes granular or foliated. Cl. in some (I), in other^r). H. =5 to 5'5; G. =3'4 to 3'6. Semitransparent; adamantine or resinous.

Yellow, brown, and green. B.B. fuses with micro-salt in the red. flame, gives reaction for titanic acid. C.c.: silica 30 ’ 6, titanic acid 40 - 8, lime 28 ’ 6. In Scotland, typical of syenites and primary limestones. In minute hair-brown crystals in the first; as at Lairg (Sutherland), Achavarasdale (Caithness), and Criffel (Kirkcudbright) (figs. 586 to 588). In the latter often in highly complex twins, yellow to brown, at Shinness (figs. 193, 589), Urquhart, Dalnain, Torbane, &c., also with ilmenite and allanite in exfiltration veins of grey granite. Dauphiné, Mont Blanc, St Gotthard, Tyrol, Arβndal, America. Greenovite, flesh-red from Glen Gairn in Aberdeenshire (like 194), and St Marcel in Piedmont; contains manganese at the latter locality.

669. Keilhauite ( Yttrotitanite), 5(CaY) (SiTi) + (AlFe) (Sifi) 3 .

Oblique prismatic, C 58°. ooP 114. Cl. -2P, 138°. H. =6 to 7; G. = 3 '5 to 3 7. Blackish brown; streak greyish yellow. B. B. with borax forms blood-red glass in the red. flame; other features like sphene. C.c.: 297 silica, 28 7 titanic acid, 21'1 lime, 10‘8 yttria, 6 ’ 2 alumina, and 6 ’ 5 iron peroxide. Near Arendal.

670. Schorlomite (Ferrotitanite), Ca 3 Si + Fe 3 Si 2 + CaTi 2 .

Cubic; ooθ and 202; generally massive; fracture conchoidal. H. = 7 to 7 , 5; G. = 3’8. Black; streak grey-black; vitreous. C.c.: silica 26, titanic acid 23 ’ 3, peroxide of iron 20, lime 29 '4. Arkansas, Kaiserstuhl, Ivaara in Finland. Perhaps a titaniferous garnet.

671. TsCHEWKINITE.

Massive; fracture flat conchoidal. H. =5 to 5'5; G. =4 ’ 5. Opaque, vitreous, splendent. Velvet-black; streak dark brown. B.B. intumesces greatly, becomes porous, and often incandesces; in white heat fuses to black glass; gelatinizes with h. acid. C.c.: 21 silica, 20 titanic acid, 11 iron protoxide, 45 peroxides of cerium metals with perhaps thoria, lime 4.

Miask, Coromandel.

672. Mosandrite.

Oblique prismatic, C 71° 24⅜'. ooP (i) 88° 36'; ∞P 0 2 (n); ooP°oo (a); -P (e ) 124° 1'; - p °° 0 (?); 0 ° pc ∞ · t: a 134° 18'; n: a 152° 52'; q: a 138° 2'. Twin face the orthopinacoid. Generally massive·. Fracture uneven. H. =4; G. =2 , 93to3. Yellowish or reddish brown; streak pale green. Vitreous to resinous lustre. C.c.: silica 29 - 9, titanic acid 9 - 9, oxide of cerium metals 26 , 5, lime 19, water 8’9. Brevig and Langesundfiord.

673. Eudialite {Eukolite), 6RSi a + RZr.

Rhombohedral; R 73° 10'. R (p), OR (α 1 ), ooP2 (⅛), iR (α 2 ); also ooR, ⅞R, -⅜R, -2R, -⅜R, R3, ⅞P2 (fig. 591). Generally massive, granular. Cl. a 1 and α 2 ; fracture uneven. H. = 5 to 5 '5; G. «= 2 ‘84 to 2 ‘95. Peachblossom-red to brownish red; streak white. Translucent; vitreous. B.B. fuses easily to a light-green opaque glass; gelatinizes in h. acid. C.c.: silica 50, zirconia 16 - 9, protoxide of iron 7, lime 11, soda 12. Kangerdluarsuk in Greenland, Sedlova-toi Island in White Sea, Brevig (Euko∙ lite), Magnet Cove in Arkansas.

674. Catapleite, 2(⅛a 2 Ca)(SiZr) 9 + 9H.

Hexagonal. P 114° 43'. OP, ooP, P, also with 2P, and ⅛P. In lamellar aggregates. Cl. prismatic and P; fracture uneven. H. = 6; G. =2 - 8. Yellowish brown to pale green; streak yellow, lustrous. C.c.: silica 467, zirconia 29 - 6, soda 10 , 8, water 9. Brevig.

675. Oerstedite.

Pyramidal. P 84° 25'. P, α>P, »Poo. Like zircon. H. — 5‘5; G. = 3 - 63. Lustre adamantine. Reddish brown. C. c.: silica 19 7, titanate of zirconia 68 ’ 96, water 5 - 6. Arendal.

676. Wohlerite, 9RSi + 3RZr + RNb.

Oblique prismatic, C 70’ 45'. α>P bθ° 14'; ooP o 2 127° 4';

- P o co 43° 18'. OP: ooP o a> 109’ 15; -P o <=o: a>P 0 a> 136° 42'; OP: ooP 103’ 31'. Crystals tabular and prismatic. Cl. clinodiagonal; fracture conchoidal. H. = 5 to 6; G. -= 3 , 4. Ligh t yellow, honeyyellow to brownish grey; streak yellowish white. C.c.: silica 28, zirconia 19, niobic acid 13’9, lime 27'8, soda 8'3, protoxide of iron 3. B.B. fuses to yellowish glass. Sol. in h. acid. Langesundfiord, Brevig.

677. Ardennite.

Right prismatic. ooP 131 β 2'; P∞ 112’ 24'; P⅞; ∞P∣; ∞P2; ooPoo; oop∞. Crystals like ilvanite. Cl. brachydiagonal, and »P. H. =6 to 7; G. =-3 62. Yellow to yellow-brown. Dichroic; brittle. C.c.: silica 27’8, alumina 24, protoxide of manganese 267, lime 2 - 2, magnesia 4 - 3, vanadic acid 3 , 2, arsenic acid 6 ’ 3, water 5. Ottrez in the Ardennes (Luxemburg).

678. Roscoelite.

Foliated masses, sometimes stellated. H. = 1; G. =2’3 to 2'9. Dark green to greenish blue. Pearly lustre. C.c.: silica 477, vanadic acid 22, alumina 14*1, magnesia 2, potash 7 ’ 6, water 5. Eldorado in California.

TITANATES WITH NIOBATES.

679. Titanomorphite, CaTi 2 .

Oblique prismatic. Like sphene. ooP, OP, ⅜P 0 α>, P 0 oo, ∣P c 2. C.c.: titanic acid 74 3, lime 25 ’ 3. Lampersdorf in Silesia, Weistritz.

680. Perovskite, CaTi.

Right prismatic. In complicated twins, often distorted, pseudo-cubic. H. = 5 - 5; G. — 4 to 4 ’ 1. Lustre metallic-adamantine. Pale yellow, reddish brown to iron-black; streak grey. C. c.: 58 ’ 8 titanic acid, 41 ’ 2 lime. B. B. with micro-salt in outer flame gives a bead greenish while hot, colourless on cooling; in inner flame grey-green when hot, violet-blue when cold. Decomposed by boiling s. acid. Zlatoust, Schelingen, Zermatt, Malenco Valley near Sondrio, Pfitsch in Tyrol, Magnet Cove in Arkansas.

681. Koppite, R 5 ⅛b 2 .

Cubic; ooO<w. G.≈4 - 45 to 4 - 56. Brown. Transparent. C.c.: niobic acid 62'46, oxide of cerium 67, oxide of lanthanum 3. Schelingen on the Kaiserstuhl in Baden.

682. Annerödite, 2R 2 Nb + 5H.∙

Right prismatic. H==6. G 57. Metallic to greasy. Black. Streak black, brown, greenish grey. Translucent in splinters; brittle. C.c.: 48niobic acid, with zirconia, thoria, ceria, yttria, and uranium oxide. Annerod near Moss (Norway).

683. Dysanalyte, 6RTi + R⅛⅛.

Cubic; ∞O∞. Cl. cubic. G. =4 ’ 13. Black. C.c.: titanic acid 41 ’ 5, niobic acid 23 - 2, cerium oxide 57, lime 19’8; protoxide of iron 5'8, soda 3 - 6. Vogtsburg on the Kaiserstuhl.

684. Pyrochlore, 5RN - b + 4R(TiTh) 2 + 4NaF.

Cubic (fig. 594). Cl. octahedral; brittle; fracture conchoidal. H. = 5; G. — 4 - 2 to 4 ’ 4. Resinous, opaque. Red-brown to black, ruby-red and transparent rarely; streak pale brown. C.c.: niobic acid 53 ’ 2, titanic acid 10 ’ 5, thoria 7 ’ 6, cerium oxide 7, lime 14 ’ 2, soda 5, fluorine 3'1. Miask, Kaiserstuhl, Brevig, and Frederiksväm. Microlite, from Chesterfield in Massachusetts, has tantalic acid 68 - 4, niobic acid 775, 117 lime and 77 protoxide of manganese. Pyrrhite from Mursinsk in the Urals, San Piero in Elba, and the Azores may be the same; at the last locality it is in orange-red octahedra, and is a niobate of zirconia.

685. Blomstrandite, (Ca,Fe), Ti + liNb 2 ⅛H.

Massive. H-5'5. G. = 4Ί7 to 4 ’ 25. Vitreous, black. Streak brown. Translucent in splinters. C.c.: niobic acid 49‘8, titanic acid 107, uranium oxide 23 7, protoxide of iron 3 ’ 3, lime 3 5, water 7’9. Nohl (Sweden).

686. Polycrase, 4RTi + Rl⅛b.

Right prismatic (fig. 595). ooP∞, ooP (140’), P, 2Pαo (56°). Fracture conchoidal. H. =5 to 6; G. =5'1. Black; streak greybrown. B.B. decrepitates violently, incandescing, but does not fuse. Sol. in s. acid. C.c.: titanic acid 26 6, niobic acid 20 ’ 4, yttria 23'3, erbia 7'5, oxide of uranium 77, water 4. Hitterö (Norway), Slettäkra in Jönköping (Sweden).

687. Euxenite, 2RTi + R⅛b + H.

Right prismatic (fig. 596). ooP (m) 140°; ooPoo (J); 2Poo (d y ) 52 β ; P (p) 102° 58'. p: b 103° 6'. Fracture conchoidal. Opaque; metallic to vitreous. Black and brownish black; streak red-brown. B. B. infusible. Not acted on by acids. C.c.: niobic acid 32, titanic acid 19'2, uranium oxide 19’5, yttria 18 ’ 2, cerium oxide 2‘8, but variable. Jölster, Tromö, Alvö, &c., in Norway; also Hitterö and Cape Lindesnaes.

688. Aeschynite.

Right prismatic. ooP (J∕) 128* 34'; 2‰ (y) 73° 16'; P (o: o) 137* 14'; o°P3 69° 23'; Poo; OP. Crystals long prismatic (fig. 597). Cl. traces; fracture imperfect conchoidal. H. = 5 to 5'5; G. — 4 - 9 to 5'1. Opaque; submetallic or resinous. Iron-black or brown; streak yellowish brown. B.B. swells and becomes yellow or brown, but is infusible. Not sol. in h. acid, partially in s. acid. C.c.: niobic and t*ntalic acids 28 - 8, titanic acid 22'6, thorium oxide 157, cerium protoxide 18'5, lanthanum oxide and didymium oxide 5 '6. Miask, Hitterö.

689. Polymignite.

Right prismatic. P (p) polar 136 β 28' and 116° 22'; ooP 109’ 46'; ooP∞; »Poo (fig. 598). Cl. macro-and brachydiagonal, imperfect; fracture conchoidal. H. = 6 '5; G. = 47 to 4'8. Opaque; semimetallic. Iron-black; streak dark brown. B.B. infusible. Sol. in h. acid. C.c.: titanic acid 46'3, zirconia 14 Ί, yttria 11 '5, lime 4‘1, iron peroxide 12'2, cerium oxide 5. Frederiksvärn.

690. Mengite, (Fe, 2r) Tι.

Right prismatic. P (e) polar angle 151’ 27' and 101’ 10'; ∞P136° 20'j ooP3; ∞Poo (fig. 599). Fracture uneven. H. = 5 to 5 '5; G. = 5'48. Opaque; semimetallic. Iron-

black; streak chestnut-brown. B. B.

infusible, but becomes magnetic. Sol. in s. acid. Miask, Groix island in Morbihan 691. Tantalite, Fe (⅜a, ⅛b).

Right prismatic. P (p) with polar edges 126° and 112’ 30', middle 91’ 42'. ooP∣ (r) 122’ 53 · ooPoo (s); ooPoo (i); poo (m) 113’ 48; 3Poo (i ) 54° 10'; ⅜Poo (n) 167’ 36'; ∣P∣ (t>); 2P2 (o).

Fracture conchoidal or uneven. H. =6 to 6 '5; G. — 6 '1 to 8. Opaque; semimetallic, adamantine, or resinous. Iron-black; streak cinnamon-or coffee-brown. B. B. infusible; scarcely affected by acids. C.c.: 76 to 50 tantalic acid, 7'5 to 29 niobic acid, 9 to 16 iron protoxide, and 1 to 6 manganese protoxide; some, with 1 to 10 tin oxide {CassiterotantaliteJ·, also in union with iron (manganese) protoxide. Kimito and Tammela in Finland, Broddbo and Finbo near Falun, and Chanteloube near Limoges; always in granite.

692. Tapiolite, 4Fe⅛a + Fe⅛fb.

Pyramidal. P middle angle 84’ 52', summit 123° 1'. H. = 6; G. — 7'2 to 7’5. Black. Lustrous. C. c.: tantalic acid 73'9, niobic acid 11'2, protoxide of iron 15. Tammela in Finland.

693. Columbite, nιFe - ⅛b + nFe⅛a.

Right prismatic. P (u) polar angles 104’ 10'and 151’, middle angle 83’ 8'; 0P (c); ooP∞ {b) ; oopoo (a); ooP tø) 135∙ 40'; a>Po 0 (m) 101’ 26'; 2P (s); 3Ï>3 (0); 3P⅜ (r); ⅜P∞ (Z) 161’; Poo (⅛) 143°; 2P00 (⅛) 112’ 26'; P∞ (i) 101’ 12'; 2P00 (e) 62’ 40'. Hemitropes, face e ; vertical axes forming an angle of 62° 40'; also on faces 2P2 (n), and rarely b. Also granular and foliated. Cl. brachydiagonal, perfect, also macrodiagonal. H.-6; G. =5'4 to 6'4. Metallic, adamantine. Iron-black to brownish; streak black or reddish brown. B.B. infusible; not affected by acids. C.c.: isomorphic mixtures of niobic and tantalic acids with protoxide of iron (or manganese). Pure columbite would give 78'8 niobic acid, pure tantalite 86 tantalic acid. The niobic acid generally prevails, and the crystals are better formed the more this is the case. Rabenstein, Bodenmais, Chanteloube, Finland, Ilmen Hills, Evigtok in Greenland, Haddam and Middletown in Connecticut, Acworth in New Hampshire, Pike’s Peak in Colorado.

694. Yttrotantalite, (Ÿ, Ca, Fe, tlj 3 (⅛a, W, ⅛b).

In two varieties, (a) Black. Right prismatic; in short prismatic or tabular crystals. ooPoo; 00P (m) 121’ 48'. 0P: 2Poo 103’ 26'; Pα>: 0P 131’ 26'; i: i 149° 42' (fig. 604); also in grains and lamellae. Cl. brachydiagonal, indistinct; fracture conchoidal or uneven. Opaque, or in thin splinters translucent. Velvet-black, semimetallic lustre, and greenish grey streak. H.-=5'5; G.=5∙4 to 57. (b) Yellow.

Amorphous, yellowish brown, or yellow, often striped or spotted; resinous or vitreous; streak white. G. — 5 - 46 to 5'88. Both varieties B.B. infusible, but become brown or yellow. Not affected by acids.

C.c.: 57 to 60 tantalic acid, 1 to 8 tungstic acid, 0 to 20 niobic acid, 20 to 38 yttria, 0'5 to 6 lime, 0'5 to 6 uranium peroxide, and 0'5 to 3'5 iron peroxide. Ytterby, and near Falun.

695. Fergusonite, (Ÿ, Êr, Ce) 3 (⅛b, Ta).

Pyramidal and hemihedric; P (s) 128° 28'. Usual form (⅛) 3P⅜ (z), P, 4∞P⅜ (? ), 0P(c) (fig. 605). 100°

54', s·.c 115’ 16', z: r 169 t, 17. Cl. traces along P; fracture imperfect conchoidal; brittle. H. =-5'5 to 6; G. =≈5'6 to 5'9. Translucent in thin splinters; semimetallic. Brownish black; streak pale brown. B. B. infusible. C.c.: chiefly niobic acid and yttria, with erbia, also a little cerium protoxide, tin oxide, uranium oxide, and iron protoxide. Cape Farewell in Greenland, Ytterby, Riesengebirge, Rockport in Massachusetts. Tyτite, from Helle near Arendal, is similar.

696. Hjelmite.

Massive, with granular fracture and traces of crystals. Η. — 5; G. =5'82. Velvet-black; streak greyish black. Lustre metallic. C.c.: tantalicacid62'4, tin 6'6, uranium 4'9, protoxide of iron 8 1, yttria 5'2. B.B. infusible. In closed tube decrepitates and yields water. Kararfvet near Falun.

697. Samarskite (Uranotantalite), (⅛ s ,fi,RJ) β (⅛>⅜a) 3 .

Right prismatic. ∞P 122’ 46'; 00 È2 95’; Pα> 93’; P; oopcc; ooPoo; 3p⅜; also in grains. Fracture conchoidal; brittle. Η. — 5'56; G. =5'6 to 576. Opaque; strong semimetallic. Velvetblack; streak dark reddish brown. B. B. fuses on the edges to a black glass. In the closed tube decrepitates, yields water, incandesces, and becomes brown. Sol. in h. acid to a gr®nish fluid.

C.c.: 37'2 niobic acid, 18'6 tantalic acid, 12 iron protoxide, 14 to 20 uranium oxide, 6 thorium oxide, 4 zirconia, and 16 yttria with lime and magnesia. Miask, Mitchell county in North Carolina. The Yttroilmenite of Hermann.

698. Nohlite, l⅛⅛b.

Massive. H —4'5 to 5; G. =5'04. Black-brown. Splintery. Brittle. Opaque; vitreous. Niobic acid 50'4, uranium oxide 14'4, zirconia 3, ferrous oxide 8, yttria 14'4, lime 4'7, water 4 6. Nohl near Kongelf (Sweden).

699. Hatchettolite.

Cubic; O, ∞O∞. Yellowish brown. Resinous lustre. Fracture conchoidal. H. = 5; G. =4'8 to 4'9. C.c.: niobic acid 34'3, tantalic acid 29’8, uranium oxide 15'5, lime 8'9, water 4’5. North Carolina.

ANTIMONIATES.

700. Romeite, Ca 3 ⅛bSb.

Pyramidal; P110° 50'. Scratches glass. G. — 47. Honey-yellow or hyacinth-red. B.B. fuses to a blackish slag. Sol. in acids. C.c.: 41'3 antimonic acid, 37 '3 antimony oxide, and 21'4 lime, but with 2 to 3 manganese and iron protoxide. St Marcel in Piedmont.

Schneebergite, from Tyrol, may be an impure variety.

701. Bleiniere, Pb(Sb, Sb) + H.

Reniform and massive. H. = 4; G. =3'9 to 4'8. Translucent; resinous to earthy. Colourless, yellow, brown, and grey. B.B. reduced on charcoal. C.c.: oxide of lead 41 to 62, antimonious acid 32 to 47, water 6 to 12. Lostwithiel, Horhausen, Nertchinsk.

702. Nadorite, Pb⅛b + PbCl 2 .

Right prismatic; ∞P 132° 5Γ. Crystals tabular. Cl. macrodiagonal. H. =3; G. = 7. Yellowish or greyish brown. Resinous to adamantine; translucent. C.c.: lead 52'2, antimony 30’8, oxygen 8, chlorine 9. Constantine (Algeria).

703. Rivotite.

Massive. Yellowish to greyish green. Opaque; fracture uneven; brittle. H. =3'5 to 4; G. — 3'6. C.c.: oxide of copper 39 - 5, oxide of silver 1'2, antimonic acid 42, carbonic acid 21. Sierra del Cadi in the province of Lerida. Thrombolite from Rezbanya, Hungary, may be a hydrated variety.

704. Mellite, A1(C 12 O 9 ) + 18H.

Pyramidal; P 93° 5'. OP; P∞; and ooPα>. Cl. P; fracture conchoidal; brittle. H. = 2 to 2'5; G. —1'5 to 1 - 6. Transparent; doubly refractive; vitreous. Honey-yellow or reddish; streak white. In closed tube yields water. B. B. chars without odour. Burns white and acts like alumina.

Sol. in n. acid or potash. C.c.: alumina 14'4, mellic acid 40 , 3, water 45 ’ 3. In lignite at Artern in Thuringia and Luschitz in Bohemia; Walchow in Moravia (cretaceous); in coal at Malovka in Tula.

705. Oxalite, 2FeG 3 + 3H.

Capillary crystals, also botryoidal or compact; fracture uneven; sectile. H. =2;G. =2'2. Opaque; resinous to dull. Straw-yellow. B.B. turns black, then red. Sol. to yellow solution in acids. C.c.: 421 iron protoxide, 42 ∙1 oxalic acid, 15 - 8 water. In lignite at Kolosoruk near Bilin, Duisburg, and Gross Almerode in Hesse.

706. Whewellite, Caθ + H.

Oblique prismatic, C 72° 41'. ∞P 100° 36'. Cl. basal, perfect; brittle. H. =2'5 to 2'8; G. = Γ838. Transparent to opaque; vitreous. Colourless. C.c.: 49'31 oxalic acid, 38'36 lime, 12'33 water. Hungary.

THE MINERAL RESINS.

Many of these are only vegetable resins slightly altered. Naphtha is fluid; the others solid, with H. =1 to 2 or 2'5. Most are amorphous, a few crystalline and monoclinic. G. = 0 '6 to 1 '6. Mostly resinous; colourless, or coloured brown, yellow, or red, with paler streak. Sol. in acids, alcohol, ether, and oils. Melt readily, and bum with flame and smoke.

707. Naphtha, Petroleum, CH 2 .

Liquid. Colourless, yellow, or brown. Transparent or translucent. G. =0’7 to 0’9. Volatilizes in the atmosphere with an aromatic bituminous odour. C.c.: 84 to 88 carbon, and 12 to 16 hydrogen. Varieties are—

Naphtha.— Very fluid, transparent, and light yellow. Tegem Lake in Bavaria, Amiano near Parma, Salies in the Pyrenees, Rangoon, Baku on the Caspian Sea, China, Persia, and North America. Used for burning, and in preparing varnishes.

Petroleum.— Darker yellow or blackish brown; less fluid or volatile. Ormskirk in Lancashire; Coalbrookdale, Pitchford, and Madeley in Shropshire; St Catherine’s Well, south of Edinburgh; Mainland of Orkney; and many other parts of Europe.

708. Elaterite (Elastic Bitumen, Mineral Caoutchouc), CH 2 .

Compact; reniform or fungoid; elastic and flexible like caoutchouc, very soft. G. = 0 '8 to 1'23. Resinous. Blackish, reddish, or yellowish brown. Strong bituminous odour. C.c.: 84 to 86 carbon, 12 to 14 hydrogen, and a little oxygen. Derbyshire, Montrelais near Nantes, and Woodbury in Connecticut.

709. Asphaltum, Bitumen.

Compact and disseminated; fracture conchoidal, sometimes vesicular; sectile. H. = 2; G. = 1 '1 to 1 '2. Opaque, resinous, and pitch-black; strong bituminous odour, especially when rubbed. Takes fire easily, and burns with a bright flame and thick smoke. Sol. in ether, except a small remainder, which is lissolved in oil of turpentine. C.c.: 76 to 88 carbon, 2 to 10 oxygen, 6 to 10 hydrogen, and 1 to 3 nitrogen. Limmer near Hanover, Seyssel on the Rhone, Vai Travers in Neufchatel, Lobsann in Alsace, in the Harz, Dead Sea, Persia, and Trinidad; Cornwall, Haughmond Hill (Shropshire), East and West Lothians, Elie and Burntisland (Fife).

710. Albertite.

Massive. Velvet-black. Adamantine lustre; brittle. C.c.: carbon 86, hydrogen 9, nitrogen 2'9, oxygen 2. Hoy, Orkney; Strathpeffer, Ross; Hillsborough, New Brunswick.

711. Piauzite.

Massive; imperfect conchoidal, sectile. H. —1’5; G. = 1'22. Dimly translucent on very thin edges; resinous. Blackish brown; streak yellowish brown. Fuses at 600° Fahr., and burns with an aromatic odour, lively flame, and dense smoke. Sol. in ether and caustic potash. Piauze near Rudolfswerth in Carniola.

712. Ixolyte.

Massive; conchoidal fracture. H. = 7; G. = 1 Ό08. Resinous. Hyacinth-red; streak ochre-yellow. Rubbed between the fingers it emits an aromatic odour; becomes soft at 119°, but is still viscid at 212°. Oberhart near Gloggnitz in Austria.

713. Amber (Succinite), C 10 H 8 O.

Round irregular lumps, grains, or drops. Fracture perfect conchoidal; slightly brittle. H. = 2 to 2 '5; G. = 1 to 1 '1. Transparent to translucent or almost opaque; resinous. Honey-yellow, hyacinth-red, brown, yellowish white; also streaked or spotted. When rubbed emits an agreeable odour, and becomes negatively electric. It melts at 550°, emitting water, an empyreumatic oil, and succinic acid; it burns with a bright flame and pleasant odour, leaving a carbonaceous remainder; only a small part is soluble in alcohol. C.c.: 79 carbon, 10 '5 hydrogen, and 10'5 oxygen. Derived chiefly from an extinct coniferous tree (Pinites succinifer), and found in the Tertiary and diluvial formations of many countries, especially northern Germany and shores of the Baltic, Sicily, Spam, and northern Italy, rarely in Britain (on the shores of Fife, Norfolk, Suffolk, and Essex, and at Kensington, near London). Used for ornamental purposes, and for preparing succinic acid and varnishes. Krantzite, from Nienburg, is essentially the same.

714. Retinite (Retinasphalt).

Roundish or irregular lumps; fracture uneven or conchoidal; very easily frangible. H. =1'5 to 2; G. = 1'05 to 1Ί5. Translucent or opaque,; resinous or glistening. Yellow or brown. Melts at a low heat, and burns with an aromatic or bituminous odour. C.c.: in general carbon, hydrogen, and oxygen, in very uncertain amount. Bovey, Halle, Cape Sable, and Osnabrück. Pyroretinite from Aussig in Bohemia is similar.

715. Walchowite, C 12 H 8 O.

Rounded pieces, with a conchoidal fracture. H. = 1 '5 to 2; G. = 1'035 to 1Ό69. Translucent, resinous. Yellow with brown stripes, and a yellowish white streak. It fuses at 482°, and burns readily. Soluble partially (7 '5 per cent. ) in ether; in s. acid forms a dark-brown solution. C.c.: 80'4 carbon, 10'7 hydrogen, and 8'9 oxygen. Walchow in Moravia.

716. Copaline ( Fossil Copal, Highgate Resin), C 40 H 64 O.

Irregular fragments. H. = 1 '5; G. = 1 '046. Translucent, resinous; burns with light yellow flame and much smoke; alcohol dissolves little of it; becomes black in sulphuric acid. C.c.: 85'54 carbon, 11'63 hydrogen, 2'76 oxygen. Highgate near London. A similar resin from Settling-Stones mine in Northumberland, found in flat drops or crusts on calc-spar, is infusible at 500° Fahr.; G. =1'16 to 1'54; it contains 85'13 carbon, 10'85 hydrogen, and 3'26 ashes.

717. Berengelite, C 40 H 62 O 8 .

Amorphous; conchoidal fracture. Dark brown, inclining to green; yellow streak. Resinous; unpleasant odour, and bitter taste. Fuses below 212°, and continues soft afterwards at ordinary temperatures; easily soluble in alcohol. C.c.: 72'40 carbon, 9'28 hydrogen, 18’31 oxygen. San Juan de Berengela in Peru.

718. Guayaquillite, C 20 H 2β O 3 .

Amorphous; yielding easily to the knife, and very friable. G. = 1'092. Pale yellow. Slightly resinous. Fluid at 212 β , viscid when cold; slightly soluble in water, and largely in alcohol, forming a yellow fluid with a bitter taste. C.c.: 77'01 carbon, 8'18 hydrogen, and 14'80 oxygen. Guayaquil in South America.

Bogbutter, from the Irish peat mosses, is similar; it melts at 124°, is easily soluble in alcohol, and contains 73'70 carbon, 12'50 hydrogen, and 13'72 oxygen.

719. Hartine, C 2o H 2o + H.

Round masses or thin layers. Brittle, but easily cut with a knife. G. = 1 '6. Resinous. Reddish brown by reflected and deep red by transmitted light; streak light brown. Becomes black on exposure. C.c.: 86'43 carbon, 8'01 hydrogen, 5'56 oxygen. In the main coal seam at Middleton near Leeds, and at Newcastle.

720. Ozocerite {Native Paraffin), CH.

Amorphous, sometimes fibrous. Very soft, pliable, and easily fashioned with the fingers. G. =0'94 to 0'97. Glimmering or glistening; semitranslucent. Yellowish brown or hyacinth-red by transmitted, dark leek-green by reflected light. Strong paraffin or aromatic odour; fuses easily to a clear oily fluid; at higher temperature burns with a clear flame, seldom leaving any ashes; readily soluble in oil of turpentine, with great difficulty in alcohol or ether. C.c.: 85'7 carbon, and 14'3 hydrogen. Binny (Linlithgow), and Edinburgh; Slanik and Zietriska in Moldavia, near Gaming in Austria, and Baku; also at Urpeth coal-mine near Newcastle-on-Tyne. Pyropissite may be a variety.

721. Hatchettine {Mineral Tallow).

Flaky, like spermaceti; or subgranular, like beeswax; soft and flexible. G. =0'6. Translucent; weak pearly. Yellowish white, wax-yellow, or greenish yellow. Greasy inodorous; readily soluble in ether. C.c.: 85'91 carbon, 14'62 hydrogen, or similar to ozocerite. Loch Fyne (fusible at 115°), Merthyr-Tydvil, Schaumburg.

722. Fichtelite, C 4 H 3 .

Crystalline (oblique prismatic) lamellae, which swim in water, but sink in alcohol. White and pearly. Fuse at 114°, but again become crystalline on cooling. Very easily soluble in ether, and precipitated by alcohol. C.c.: 88 '9 carbon and 11 '1 hydrogen. In pine wood in a peat-moss near Redwitz in Bavaria.

723. Hartite, C 6 H 5 .

Anorthic; but mostly like spermaceti or white wax, and lamellar. Sectile, but not flexible. H. = 1; G. = 1 046. Translucent; dull resinous. White. Melts at 165°, and burns with much smoke. Very soluble in ether, much less so in alcohol. C.c.: 87'8 carbon, and 12'2 hydrogen. Oberhart in Austria.

724. Konlite, C a H.

Crystalline folia and grains. Soft. G. = 0 '88. Translucent; resinous. White, without smell. Fuses at 120° to 137°. Sol. in n. acid; precipitated by water in a white crystalline mass. C.c.: 92'3 carbon, 7'7 hydrogen. Uznach near St Gall, Redwitz.

725. ScHEERERITE, CH 2 .

Oblique prismatic; tabular or acicular. Soft and rather brittle. G. =1 to 1'2. Translucent; resinous or adamantine. White, inclining to yellow or green. Feels greasy, has no taste, and when cold no smell, but when heated a weak aromatic odour. Insoluble in water; readily sol. in alcohol, ether, and n. and s. acids. C.c.: 75 carbon, 25 hydrogen. Uznach. Branchite, white, translucent, fusing at 167°, is similar; Montevaso in Tuscany.

726. Idrialite, C s H 2 .

Massive; fracture uneven or slaty; sectile. H. =1 to 1'5; G. =1'4 to Γ6 (Γ7 to 3'2). Opaque; resinous. Greyish or brownish black; streak blackish brown, inclining to red. Feels greasy. Burns with a thick smoky flame, giving out sulphurous acid, and leaving some reddish brown ashes. C.c.: 77 idrialine ( = 94'7 carbon and 5'3 hydrogen) and 18 cinnabar, with a little silica, alumina, pyrite, and lime. The idrialine may be extracted by warm olive oil or oil of turpentine as a pearly shining mass, difficultly fusible. Idria.

727. Torbanite.

Massive; fracture subconchoidal. Yellow, brown-grey, and light brown. H. = 1 , 5 to 2; G. = 1 '28. C.c.: 60 to 65 carbon, 9 hydrogen, 4 to 5 oxygen, 10 to 20 silicate of alumina. When distilled below redness yields a burning fluid holding paraffin in solution; above redness a large quantity of highly illuminating gas. Shown by the microscope to consist of granules of a yellow bituminoid wax, with interstitial shaly matter. Torbanehill in Scotland, Pilsen in Bohemia, Kurakina and Murayevna in Russia.

728. Dopplerite.

Jelly-like elastic masses. Brownish black; streak brown. Greasy lustre. H.—0'5; G. =1 ’ 1. After drying H. =2'5; G. —1'5. Insoluble in alcohol and ether. An acid substance related to humic acid. From peat beds, Aussee (Styria) and Switzerland.

THE COALS.

729. Anthracite {Glance Coal).

Massive and disseminated; rarely columnar. Fracture conchoidal; brittle. H. =2 to 2'5; G. = 1'4 to 1'7. Opaque; brilliant metallic. Iron-black; streak unaltered. Perfect conductor of electricity. Burns difficultly with a very weak or no flame, and does not cake; in the closed tube yields a little moisture, but no empyreumatic oil; detonates with nitre. C.c.: carbon above 90 per cent., with 1 to 3 oxygen, 1 to 4 hydrogen, and 0 to 3 nitrogen; and ashes chiefly of silica, alumina, lime, and peroxide of iron. Common in some parts of all coal-fields; and especially in the United States, as in Rhode Island, Massachusetts, and above all in Pennsylvania. Used chiefly for manufacturing metals.

730. Common Coal {Black Coal, Stone or Mineral Coal, Bitu minous Coal).

Compact, slaty, or confusedly fibrous; often dividing into rhomboidal, columnar, or cubical fragments. Fracture conchoidal, uneven, or fibrous; rather brittle or sectile. H. =2 to 2 '5; G. = 1 '2 to 1 '5. Vitreous, resinous, or silky in the fibrous variety. Blackish brown, pitch-black, or velvet-black. Burns easily, emitting flame and smoke, with a bituminous odour; heated in the closed tube yields much oil. C.c.: 74 to 90 carbon, with 0'6 to 8 or 15 oxygen, 3 to 6 hydrogen, 0 to 1 to 2 nitrogen, 0'1 to 3 sulphur, and 1 to 11 earthy matters or ash, in 100 parts.

Slate Coal or Splint has a thick slaty structure, and an uneven fracture. Cherry Coal is the name applied to the brittle highly lustrous variety common in the English coal-fields. Caking Coal is a more bituminous variety which undergoes semifusion when ignited, caking or agglutinating during combustion. Cannel Coal has a resinous, glimmering lustre, and a flat-conchoidal fracture, breaks into irregular cubical fragments, but is more solid and takes a higher polish than other varieties. This burns with a bright flame, and yields much gas. Abundant in many lands, as in England, Scotland, and Ireland, in Belgium and France, in Germany and southern Russia. British America and the United States possess immense fields, especially in the valley of the Mississippi. Also found in China, Japan, Hindustan, Australia, Borneo, and several of the Indian islands.

731. Lignite {Jet, Brown Coal).

Distinctly vegetable in origin,—the external form, and very often the internal woody structure, being preserved. The texture is compact, woody, or earthy. Fracture conchoidal, woody, or uneven; soft and often friable. G. ≈0'5 to 1'5. Lustre sometimes resinous, mostly glimmering or dull. Brown, black, or rarely grey. Burns easily with an unpleasant odour; colours solution of potash deep brown. C.c.: 47 to 73 carbon, 2'5 to 7'5 hydrogen, 8 to 33 oxygen (with nitrogen), and 1 to 15 ashes. Jet is pitch-black, with conchoidal fracture and resinous lustre. Brown coal occurs at Bovey-Tracy in Devonshire; also in Germany, Hungary, France, Italy, and Greece. The Surturbrand of Iceland seems a variety. Used as fuel, but much inferior to common coal. The Oolitic coals of Yorkshire, Antrim, Brora, Mull, and Skye are intermediate varieties. [table]

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