Cryolite

Cryolite; Na3AlF6. — Color, snow-white or ice-like, sometimes reddish, brownish, or even black; luster, glassy and greasy; H = 2.5; G = 2.95 to 3; cleavage, perfect; looks rather like quartz, but distinguished by softness and good cleavage; composition, a fluoride of sodium and aluminum. Used as a solvent in the manufacture of aluminum. Aluminum oxide, Al2O3, made from bauxite, is dissolved in melted cryolite, and the aluminum is then deposited by an electric current. Also used for making enamels and opaque glass. Value, about $2000 per ton. Found in quantity, so far, only in one place, at Ivigtut, Greenland, in a granite dike in gneiss.