1. A mineral consisting of a homogeneous ground with crystals of some other mineral imbedded, giving to the mass a speckledcomplexion. One variety of Egyptian porphyry has a purple ground, whence the name of the species; but the homogeneous ground with imbedded crystals, being all that is essential to porphyry its composition and colors are consequently various.
2. Porphyry is very hard, and susceptible of a fine polish.
3. Porphyry is composed of paste in which are disseminated a multitude of little angular and granuliform parts, of a color different from the ground.
A term used somewhat loosely to designate a rock consisting of a fine-grained base (usually feldspathic) through which crystals, as of feldspar or quartz, are disseminated. There are red, purple, and green varieties, which are highly esteemed as marbles.
PORPHYRY, a name originally applied to a reddish or purple rock (τropφυpeoς, purple) found in Upper Egypt, principally at Jebel Dokhan, and much used by the ancients as a decorative stone. This porphyry, the porfido rosso antico of Italian antiquaries, consists of a dark crimson or chocolate-coloured felsitic base, with disseminated crystals of white felspar, probably oligoclase. It was a favourite material with Roman sculptors under the lower empire, and notwithstanding its excessive hardness was worked into large sarcophagi and other objects, ornamented in some cases in elaborate relief. This porphyry was also ingeniously used for the lower part of the busts of Roman emperors, the head being executed in another material, while the porphyry was used for the drapery, the colour of the stone suggesting that of the imperial purple. The antique red porphyry is often confounded with the rosso antico, which, being merely a red marble, is a much softer stone....
The term “porphyry” has been gradually extended to a variety of rocks which contain distinct crystals of any mineral sprinkled through a fine-grained ground. Among the best known of the ancient porphyries is the porfido verde antico, or lapis Lacedaemonius, a beautiful rock with pale-green crystals of labrador-felspar, found at Mount Taygetus in the Morea. The meaning of the word ‘ ‘ porphyry” has become so vague, in consequence of its application to many rocks widely differing from each other in composition, that there is a tendency among modern petrologists to abandon its use as a substantive, and merely to retain the adjective “porphyritic” as a convenient designation for all rocks which exhibit a structure like that of the ancient porphyry. Any rock, whatever its mineralogical composition, may therefore become porphyritic by containing isolated crystals developed in a compact or micro-crystalline matrix. Among the finest rocks of this class in
Britain are the porphyritic granites of Cornwall and of Shap in Westmoreland; the el vans, or quartz-porphyries (see vol. x. p. 233), which occur as dykes cutting through the slates and granites of Cornwall; the peculiar rock termed “luxullianite” (see vol. xi. p. 49); and the green and red porphyritic felstones of Cumberland. A beautiful brown porphyriticfelstone occurs at Buchan Ness, on the coast of Aberdeenshire; while a rock closely resembling the antique green porphyry is found on Lambay Island, near Dublin. For a description of porphyrite, see vol. x. p. 234.
PORPHYRY (c. 233-306). See Neoplatonism, vol. xvii. p. 336 sq.
9th ed. Encyclopædia Britannica, vol. 19, p. 521 [401 words — estimated reading time: 3 minutes]
An animal or shell of the genus Murex. It is of the snail kind, the shell consisting of one spiral valve. From one species of this genus was formerly obtained a liquor that produced the Tyrian purple.
Where were white, green, and blue, hangings, fastened with cords of fine linen and purple to silver rings and pillars of marble: the beds were of gold and silver, upon a pavement of red, and blue, and white, and black, marble.
Hangings of white and blue linen were fastened with cords of fine white and purple material to silver rings on the marble pillars. Gold and silver couches were arranged on a mosaic pavement of porphyry, marble, mother-of-pearl, and other costly stones.
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