Fluor Spar

Fluor Spar, or FLUORITE, a mineral which has been often described as chemically fluorite of lime, a compound of fluoric (hydrofluoric) acid and lime, but which is in reality calcium fluoride, $\backslash text\{CaF\}\_2$, consisting of 48.72 calcium, and 51.18 fluorine; occasionally it also contains some calcium chloride, and now and again organic matter, which is sometimes so abundant that when the mineral is struck with a hammer it emits a fetid odour—hence the name fetid-spar (Ger. stink-fluss). Fluor spar occurs both crystallised and massive, the massive varieties exhibiting a crystalline structure; the crystals appear usually in groups, sometimes of the primary form, which is a cube, but often of secondary forms, of which there is great variety, as the octahedron, rhombic dodecahedron, &c. Fluor spar is sometimes colourless, but often green, blue, yellow, or red, more rarely gray, or even black, different shades of colour frequently appearing in the same specimen, and in the massive varieties beautifully intermixed. Its colours often rival those of the most beautiful gems; but it is of very inferior hardness, being scratched even by quartz. Its specific gravity is 3.15 to 3.20. It generally becomes phosphorescent when heated, although this is more remarkably the case with some varieties than with others; it is decomposed by heated sulphuric acid, with evolution of hydrofluoric acid as a pungent gas; and, this having the property of acting upon and corroding glass, fluor spar is used with sulphuric acid for etching on glass. Fluor spar is also used for ornamental purposes, being wrought into vases, &c., for which it was in high esteem among the ancients. But the greater abundance in which it is now obtained has diminished the value of ornaments made of it. It is very commonly associated with ores of tin, silver, lead, and copper, occurring chiefly in veins, but is also found by itself in drusy cavities in granite and in veins in crystalline schists, slate, limestone, and sandstone. It has been met with also in volcanic tuff in Italy and in cannel coal in the United States, where it is limited to two districts in Illinois and Indiana. It is found only in a few places in Scotland, and in insignificant quantity, but is nowhere more abundant than in England, particularly in Derbyshire and in Cornwall. In Cornwall it is used as a flux for reducing copper ore. In Derbyshire the blue massive variety is known to the miners as Blue John. The manufacture of ornaments of fluor spar is carried on to some extent in Derbyshire; and fluor spar is often called Derbyshire spar.