Cryolite

Cryolite, a mineral which exists in great abundance on the coast of Greenland. It consists mainly of a fluoride of aluminium in combination with Fluoride of Sodium, $6\backslash text\{NaF\}\backslash cdot\backslash text\{Al\}\_2\backslash text\{F\}\_6$. The metal Aluminium (q.v.) was formerly largely obtained from it, but it is now most important as a source of alum and of soda bicarbonate; much of it, also, is melted and made into a kind of glass.