FLUOR-SPAR, a mineral which has been often described as chemically fiturte of lime, a compound of fluoric (hydrofluoric) acid and lime, but which is in reality fluoride of calcium (CaF), consisting of 48.14 fluorine and 51.86 calcium (the base of lime). It occurs both crystallized and massive; the massive varieties exhibiting a crystalline structure; the crystals 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, etc. F. S. is sometimes colorless, but often green, blue, yellow, or red, more rarely gray, or even black; different shades of color frequently appearing in the same specimen, and in the massive varieties beautifully intermixed,. Its colors often rival those of the most beatiful gems; but it is of 'very inferior hardness, being scratched even by quartz. Its specific gravity is 3.14. It generally becomes phos phorescent 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 hydro fluoric acid as a pungent gas, which, having the property of acting upon and corroding glass, F. S. is used with sulphuric acid for etching on glass. F. S. is also used for
ornamental purposes, being wrought into vases, etc., for which it was in high esteem among the ancients. But the greater abundance in which it is now obtained has dimin ished 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 drnsy cavities in granite, sreenstone, etc. It is found only in a few places in Scotland, and in insignificant quantity, but is nowhere more abundant than in England. particu larly- in Derbyshire and in Cornwall. In Cornwall, it is used as a flux for reducing copper ore. Derbyshire, the blue massive variety is known to the miners as Blue John. The manufacture of ornaments of F. S. is carried on to some extent in Derby shire. F. S. is often called DERBYSHIRE SPAR.