CRYOLITE  , a

mineral discovered in Greenland by the Danes in 1794, and found to be a compound of fluorine, sodium and aluminium . From its general appearance, and from the fact that it melts readily, even in a candle-flame, it was regarded by the Eskimos as a peculiar kind of ice; from this fact it acquired the name of cryolite (from Gr. icpboc, frost, and ki.Bos, stone) . Cryolite occurs in colourless or snow-white cleavable masses, often tinted brown or red with iron oxide, and occasionally passing into a black variety . It is usually translucent, becoming nearly transparent on immersion in water . The mineral cleaves in three rectangular directions, and the crystals occasionally found in the crevices have a cubic habit, but it has been proved, after much discussion, that they belong to the anorthic system . The hardness is 2.5, and the specific gravity 3 . Cryolite has the formula Na3AIF6, or 3NaF•AlF3, corresponding to fluorine 54.4, sodium 32.8, and aluminium 12.8% . It colours a flame yellow, through the presence of sodium, and when heated with sulphuric acid it evolves hydrofluoric acid . Cryolite occurs almost exclusively at Ivigtut (sometimes written Evigtok) on the Arksut Fjord in S.W . Greenland . There it forms a large deposit, in a granitic vein running through gneiss, and is accompanied by quartz, siderite, galena, blende, chalcopyrite, &c . It is also associated with a group of kindred minerals, some of which are evidently products of alteration of the cryolite, known as pachnolite, thomsenolite, ralstonite, gearksutite, arksutite, &c .

Cryolite likewise occurs, though only to a limited extent, at Miyask, in the Ilmen Mountains; at

Pike's Peak, Colorado, and in the Yellowstone Park . Cryolite is a mineral of much economic importance . It has been extensively used as a source of metallic aluminium, and as a flux in smelting the metal . It is largely employed in the manufacture of certain sodium salts, as suggested by Julius Thomsen, of Copenhagen, in 1849; and it has been used for the production of certain kinds of porcelain and glass, remarkable for its toughness, and for enamelled ware . Although cryolite is known as ice-stone " (Eisstein), it is not to be confused with "ice-spar" (Eisspath), which is a vitreous kind of felspar termed " glassy felspar" or rhyacolite_ (F . W .