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Cryolite

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CRYOLITE, krn-lit (Gr. lice-stone," in allusion to its translucent whiteness), a native fluoride of aluminum and sodium, having the formula 3NaF.AlFs. It crystallizes in the mono clinic system, and also occurs massive. It is transparent or translucent, and the purer varie ties are colorless or white. Its lustre is vitreous, and it has a hardness of 2.5 and a specific grav ity of about 3. The best-known deposit of cryo lite is in West Greenland, whence large quanti ties of it have been taken for use in the prepara tion of metallic aluminum. Less important de posits are also known in the Urals, and in El Paso County, Colo. Cryolite is also used in the manufacture of alum, soda and certain kinds of glass, notably the so-called °milk-glass," or hot-cast porcelain, which is composed of cryo lite, silica and oxide of zinc. The only com mercial supply of cryolite is the great mine at Ivigtut, where two gtades are produced, known to the trade as °white cryolite" and °black cryolite." The discoloration of the latter is due

to its large admixture of fluorite. In recent years only the black cryolite has been imported into the United States. The importations for 1916 amounted to 3,857 tons, valued at $42.84 per ton, as compared with 3,949 tons valued at $21 per ton for 1915. The latter price is about the average for the last 10 years, the increased price for .1916 being due to the greatly ad vanced rates for ocean tonnage caused by the war. An excellent description of the cryolite mine at Ivigtut may be found in The Mining Magazine (London) for April 1916. Consult also United States Geological Survey,