Cryolite

cryolite or kryolite (both: krī`əlīt') [Gr.,=frost stone], mineral usually pure white or colorless but sometimes tinted in shades of pink, brown, or even black and having a luster like that of wax. Chemically, it is a double fluoride of sodium and aluminum, Na₃AlF₆. Its principal use is as a flux in the smelting of aluminum. It is used also as a source of soda, aluminum salts, fluorides, and hydrofluoric acid (by the action of sulfuric acid). It was discovered in Greenland in 1794 and occurs almost nowhere else. Cryolite has been produced synthetically.

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cryolite [′krī·ə‚līt]

(mineralogy)

Na₃AlF₆A white or colorless mineral that crystallizes in the monoclinic system but has a pseudocubic aspect; found in masses of waxy luster; hardness is 2.5 on Mohs scale, and specific gravity is 2.95-3.0; used chiefly as a flux in producing aluminum from bauxite and for making salts of sodium and aluminum and porcelaneous glass. Also known as Greenland spar; ice stone.

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Cryolite 

a mineral from the group of natural fluorides, with chemical composition Na₂NaAlF₆.

In cryolite’s structure, the Al and one-third of the Na are located in the center of the AlF₆ and NaF₆ octahedrons, while two-thirds of the Na is in the center of the NaF₁₂ polyhedrons. The mineral crystallizes in the monoclinic system; cubic crystals are rare. Ordinarily, colorless, white, or gray crystal aggregates with a vitreous luster form. Cryolite has a hardness of 2.5–3.0 on the mineralogical scale and a density of 2,960–2,970 kg/m³. It is found in metasomatically displaced pegmatites and is formed from fluoride-enriched hot water solutions associated with alkaline granites. Industrial deposits are rare (Ivigtut in western Greenland).

Cryolite is used extensively in aluminum metallurgy; it is also used to obtain enamels and for other purposes. Most of the cryolite used in industry is obtained synthetically [by the interaction of the sulfates of Al and NaF; by neutralization of gaseous fluosilicic acid (H₂SiF₆) with aluminum hydroxide and NaOH].

The mineral is called cryolite because of its resemblance in luster and refractive index to ice. Some scientists use the term “cryolite” for all varieties of ice (ice, snow, hail); but others, only for ice, as a monomineral rock.