Cryolite (sodium3aluminiumfluorine6, sodium hexafluoroaluminate) is a rare mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987.
It is used in the reduction ("smelting") of aluminium, in pest control, and as a dye.
History
Cryolite was first described in 1798 by Danish veterinarian and physician (1740–1801),
[ (At the ordinary session of the Danish Royal Society of Science on February 1st of this year, Prof. Abildgaard presented a report about Norwegian titanium ores and about the analysis of them undertaken by him. He also communicated a notice of an especially white, spar-like mineral that was brought several years ago from Greenland to Denmark. According to an investigation performed on it, it consists of alumina and hydrofluoric acid. A compound of which no similar example in the mineral realm has yet been found. It received the name "cryolite" because under a blowpipe, it melts like frozen brine.)][ (He has named this Greenlandic stone cryolite or ice stone on account of its appearance, and because it melts so easily under a blowpipe.)] from rock samples obtained from local
Inuit who used the mineral for washing their hides; the actual source of the ore was later discovered in 1806 by the explorer Karl Ludwig Giesecke.
who found the deposit at Ivigtut (old spelling) and nearby Arsuk Fjord, Southwest Greenland, where it was extracted by Øresund Chemical Industries.
[The Brazilian statesman and scientist José Bonifácio de Andrada e Silva also analyzed cryolite:
]
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Cryolite ( Chryolit) is discussed on pp. 37–38. From p. 38: "Dieses sonderbare Fossil besteht aus Thonerde, Fluẞspathsäure und ein klein wenig Kali. Er kommt vor in Grönland, … " (This strange mineral consists of alumina, hydrofluoric acid and a very little potassium carbonate. It occurs in Greenland, … )
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Reprinted in French:
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Reprinted in English: See "Chryolite" on pp. 212–213.
The name is derived from the
Greek language words cryos (), and lithos ().
[Albert Huntington Chester, A Dictionary of the Names of Minerals Including Their History and Etymology (New York, New York: John Wiley & Sons, 1896), p. 68.]
The Pennsylvania Salt Manufacturing Company used large amounts of cryolite to make caustic soda and fluorine compounds, including hydrofluoric acid at its Natrona, Pennsylvania, works, and at its integrated chemical plant in Cornwells Heights, Pennsylvania, during the 19th and 20th centuries.
It was historically used as an ore of aluminium and later in the electrolytic processing of the aluminium-rich oxide ore bauxite (itself a combination of aluminium oxide minerals such as gibbsite, boehmite and diaspore). The difficulty of separating aluminium from oxygen in the oxide ores was overcome by the use of cryolite as a flux to dissolve the oxide mineral(s). Pure cryolite itself melts at 1012 °C (1285 K), and it can dissolve the aluminium oxides sufficiently well to allow easy extraction of the aluminium by electrolysis. Substantial energy is still needed for both heating the materials and the electrolysis, but it is much more energy-efficient than melting the oxides themselves. As natural cryolite is now too rare to be used for this purpose, synthetic sodium aluminium fluoride is produced from the common mineral fluorite.
In 1940 before entering World War II, the United States became involved with protecting the world's largest cryolite mine in Ivittuut, Greenland from falling into Nazi Germany's control.
In 1987 the main mining in Ivittuut was closed. According to economist Arindam Banerjee, exploitation of cryolite in Greenland contributed to nearly 54 billion euros to Danish economy,
Source locations
Besides
Ivittuut, on the west coast of
Greenland where cryolite was once found in commercial quantities, small deposits of cryolite have also been reported in some areas of
Spain, at the foot of
Pikes Peak in
Colorado, Francon Quarry near
Montreal in
Quebec,
Canada and also in Miask,
Russia.
Uses
Molten cryolite is used as a solvent for
aluminium oxide (Al
2O
3) in the Hall–Héroult process, used in the refining of
aluminium. It decreases the melting point of aluminium oxide from 2000–2500 °C to 900–1000 °C, and increases its conductivity
thus making the extraction of aluminium more economical.
Cryolite is used as an insecticide and a pesticide.
Physical properties
Cryolite occurs as glassy, colorless, white-reddish to gray-black prismatic
monoclinic crystals. It has a
Mohs hardness of 2.5 to 3 and a
specific gravity of about 2.95 to 3.0. It is translucent to transparent with a very low
refractive index of about 1.34, which is very close to that of
water; thus if immersed in water, cryolite becomes essentially invisible.
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