Cryolite

Cryolite is a rare mineral identified with the chemical formula Na₃AlF₆, which consists of sodium, aluminum, and fluorine. Cryolite was historically used in the industrial production of aluminum, but its role has largely been replaced by synthetic compounds.

History

Cryolite was first described in 1798 by Johan Gottlieb Gahn and Jöns Jakob Berzelius in Ivigtut, Greenland. The name Cryolite originates from the Greek words 'kruos' meaning frost, and 'lithos' meaning stone.

Properties

Cryolite is a colorless to white mineral that can also exhibit a brownish hue. It has a Mohs hardness of 2.5 to 3 and a specific gravity of about 2.95 to 3.0. It is transparent to translucent with a low refractive index of about 1.338, which is very close to that of water; hence if immersed in water, cryolite becomes virtually invisible.

Uses

Historically, cryolite was used in the Hall-Héroult process to reduce the melting point of aluminum oxide. This allowed for the more efficient extraction of aluminum from its ore. However, due to the rarity of cryolite, it has been largely replaced by synthetic sodium aluminum fluoride.

Occurrence

Cryolite occurs as vein fillings in the Ivigtut Cryolite deposit in Greenland. This deposit was the only economically important source of cryolite and was mined until it was depleted in 1987. Cryolite has also been reported in small quantities from locations in the United States, including Colorado and Utah.

See also

• List of minerals
• Fluoride
• Aluminum

References

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Cryolite

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  Ivigtut Cryolite

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  Cryolite Mine Ivigtut Greenland

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  Cryolite Unit Cell 3D Polyhedra