FLUOR SPAR, Fluorite, or Calcium Fluoride, CaF 2 , (Germ. Fluss-spatlι), the “blue John” of Derbyshire, and “cann” or “kann” of Cornish miners, occurs crystallized in simple or modified cubes and octahedrons; also nodular, compact and granular, and more rarely fibrous, or soft and earthy. Some octahedral crystals from the mines of St Agnes, in Cornwall, are made up of minute cubes, which may themselves show faces of other forms of the monometric system of crystallography. Fluor spar is a brittle, transparent to sub-translucent mineral, with a perfect octahedral cleavage, a vitreous, sometimes splendent lustre, a hardness of 4, and a specific gravity of 3Ol-3 ’ 25. Before the blowpipe it decrepitates, tinges the flame dull red, and fuses into an enamel. Heated with concentrated sulphuric acid it yields hydrofluoric acid (see Chemistry, vol. v. p. 491). In colour fluor spar varies much, being blue, purple, green, yellow, pink, or brown; it is sometimes dichroic. The colours are attributed by Wyrouboff to the presence of minute quantities of hydrocarbons, taken up from solutions from which the mineral has crystallized; by others they are considered to be due to peculiarities of molecular structure. In the Weardale fluors small cavities containing liquid have occasionally been found. Fluor spar, in common with some other substances, when exposed to light, or when raised to a temperature somewhat under redness, usually phosphoresces, emitting a bright light, the colour of which is not dependent on that of the mineral. A variety of fluor spar has received its name chlorophane from its fine green phosphorescence. Like the colour, the phosphorescence of fluor-spar is destroyed by exposure to a high temperature; it may be partly restored by means of an electric ...