Biology:Cryolite

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Cryolite
Cryolite from Ivittuut, Greenland
General
CategoryHalide mineral
Formula
(repeating unit)		Na3AlF6
Strunz classification3.CB.15
Dana classification11.6.1.1
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/n
Unit cella = 7.7564(3) Å,
b = 5.5959(2) Å,
c = 5.4024(2) Å; β = 90.18°; Z = 2
Identification
Formula mass209.9 g mol−1
ColorColorless to white, also brownish, reddish and rarely black
Crystal habitUsually massive, coarsely granular. The rare crystals are equant and pseudocubic.
TwinningVery common, often repeated or polysynthetic with simultaneous occurrence of several twin laws
CleavageNone observed
FractureUneven
TenacityBrittle
Mohs scale hardness2.5 to 3
|re|er}}Vitreous to greasy, pearly on {001}
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.95 to 3.0.
Optical propertiesBiaxial (+)
Refractive indexnα = 1.3385–1.339, nβ = 1.3389–1.339, nγ = 1.3396–1.34
Birefringenceδ = 0.001
2V angle43°
Dispersionr < v
Melting point1012 °C
SolubilitySoluble in AlCl3 solution, soluble in H2SO4 with the evolution of HF, which is poisonous. Insoluble in water.[1]
Other characteristicsWeakly thermoluminescent. Small clear fragments become nearly invisible when placed in water, since its refractive index is close to that of water. May fluoresce intense yellow under SWUV, with yellow phosphorescence, and pale yellow phosphorescence under LWUV. Not radioactive.

Cryolite (Na3AlF6, sodium hexafluoroaluminate) is a rare mineral identified with the once-large deposit at Ivittuut on the southwest coast of Greenland, mined commercially until 1987.[3]

It is used in the reduction ("smelting") of aluminium, in pest control, and as a dye.

History

Peter Christian Abildgaard

Cryolite was first described in 1798 by Danish veterinarian and physician Peter Christian Abildgaard (da) (1740–1801),[4][5] 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.[6][7] who found the deposit at Ivigtut (old spelling) and nearby Arsuk Fjord, Southwest Greenland, where it was extracted by Øresund Chemical Industries.[8] The name is derived from the Greek words cryos (Greek: κρύος, lit. 'frost'), and lithos (Greek: λίθος, lit. 'stone').[9]


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).


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.[10]

In 1987 the main mining in Ivittuut was closed. According to economist Arindam Banerjee, exploitation of cryolite in Greenland contributed nearly 54 billion euros to Danish economy,[11] though this claim has been strongly disputed.[12]

Source locations

The cryolite mine at Ivigtut, Greenland, summer 1940

Besides Ivittuut, on the southwest 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 Miass, Russia.[13][14]

Uses

Molten cryolite is used as a solvent for aluminium oxide (Al2O3) 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[15] thus making the extraction of aluminium more economical.[16]

Cryolite is used as an insecticide and a pesticide.[17] It is also used to give fireworks a yellow color.[18] It is used in glass manufacturing as a "powerful opaliser."[19]

Physical properties

Cryolite's unit cell. Fluorine atoms (yellow) are arranged in octahedra around aluminium atoms (red). Sodium ions (purple) occupy the interstices between the octahedra.

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.[20]

References

  1. ↑ CRC Handbook of Chemistry and Physics, 83rd Ed., p. 4–84.
  2. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W. 
  3. ↑ "Eclipse Metals buys unique historical cryolite mine in Greenland". 15 January 2021. https://im-mining.com/2021/01/15/eclipse-metals-buys-unique-historical-cryolite-mine-greenland/. 
  4. ↑ Abildgaard (1799). "Norwegische Titanerze und andre neue Fossilien" (in German). Allgemeines Journal der Chemie 2: 502. https://books.google.com/books?id=d5YMAQAAIAAJ&pg=PA502. "In der ordentlichen Versammlung der königl. Gesellschaft der Wissenschaften am 1. Februar dieses Jahres stattete Hr. Prof. Abildgaard einen Bericht über die Norwegischen Titanerze und über die von ihm mit denselben angestellten Analysen ab. Zugleich theilte er auch eine Nachricht von einer vor wenigen Jahren aus Grönland nach Dänemark gebrachten besonders weißen spathartigen Miner mit. Einer damit angestellten Untersuchung zu folge bestand sie aus Thonerde und Flußspathsäure. Eine Verbindung, von welcher noch kein ähnliches Beyspiel im Mineralreich vorgekommen ist. Sie hat den Namen Chryolit erhalten, weil sie vor dem Löthrohre wie gefrorne Salzlauge schmilzt.".  (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.)
  5. ↑ Abildgaard, P. C. (1800). "Om Norske Titanertser og om en nye Steenart fra Grönland, som bestaaer af Flusspatsyre og Alunjord" (in Danish). Det Kongelige Danske Videnskabers-Selskabs (The Royal Danish Scientific Society). 3rd series 1: 305–316. http://babel.hathitrust.org/cgi/pt?id=umn.31951d00004536u;view=1up;seq=333. "[From p. 312] Han har kaldt denne grönlandske Steen Kryolith eller Iissteen formedelst dens Udseende, og fordi den smelter saa meget let for Blæsröret.".  (He has named this Greenlandic stone cryolite or ice stone on account of its appearance, and because it melts so easily under a blowpipe.)
  6. ↑ The Mineral Collector. Mineral Collector Company. 1903. https://books.google.com/books?id=8Ynwkqa908oC&dq=Cryolite%20giesecke&pg=PA157. 
  7. ↑ Engineering and Mining Journal-press. McGraw-Hill Publishing Company. 1926. https://books.google.com/books?id=oX4cAQAAMAAJ&dq=Cryolite%20Giesecke&pg=PA238. 
  8. ↑ The Brazilian statesman and scientist José Bonifácio de Andrada e Silva also analyzed cryolite:
  9. ↑ 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.
  10. ↑ Magazine, Smithsonian. "How This Abandoned Mining Town in Greenland Helped Win World War II" (in en). https://www.smithsonianmag.com/travel/how-abandoned-mining-town-greenland-helped-win-world-war-ii-180973835/. 
  11. ↑ Sandré, Tanguy (3 March 2025). "Cryolite: le Danemark censure son histoire coloniale". Mediapart. https://blogs.mediapart.fr/tanguy-sandre/blog/030325/cryolite-le-danemark-censure-son-histoire-coloniale. 
  12. ↑ Kajkus, Ines; Lindberg, Kristian (2025-02-10). "Vrede kilder beskylder DR for at manipulere seerne i sprængfarlig dokumentar: »Grebet ud af den blå luft«" (in da). https://www.berlingske.dk/kultur/vrede-kilder-beskylder-dr-for-at-manipulere-seerne-i-spraengfarlig. 
  13. ↑ "Cryolite (Sodium Aluminum Fluoride)". http://www.galleries.com/Cryolite. 
  14. ↑ "Cryolite | mineral" (in en). https://www.britannica.com/science/cryolite. 
  15. ↑ Cassayre, Laurent; Palau, Patrice; Chamelot, Pierre; Massot, Laurent (11 November 2010). "Properties of Low-Temperature Melting Electrolytes for the Aluminum Electrolysis Process: A Review". Journal of Chemical & Engineering Data 55 (11): 4549–4560. doi:10.1021/je100214x. https://hal.archives-ouvertes.fr/hal-03474327/file/Cassayre_5793.pdf. 
  16. ↑ Totten, George E.; MacKenzie, D. Scott (2003). Handbook of Aluminum: Volume 2: Alloy production and materials manufacturing. vol. 2. New York, NY: Marcel Dekker, Inc.. ISBN 0-8247-0896-2. 
  17. ↑ Rao, J.R.; Krishnayya, P.V.; Rao, P.A. (2000). "Efficacy of cryolite against major lepidopteran pests of cauliflower". Plant Protection Bulletin 52 (3/4): 16–18. ISSN 0378-0449. https://www.cabdirect.org/cabdirect/abstract/20013171514. Retrieved 17 June 2021. 
  18. ↑ Helmenstine, Anne Marie. "How Firework Colors Work and the Chemicals That Make Vivid Colors" (in en). https://www.thoughtco.com/chemistry-of-firework-colors-607341. 
  19. ↑ "The Chemical Calculation of Glass Compositions, p. 713 (March, 1925)". "Glass" (Industry Periodical). 1924. https://books.google.com/books?id=HZ0kAQAAMAAJ&dq=cryolite%20opaliser&pg=PA713. 
  20. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Hurlbut



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