cryolite
{{Short description|Halide mineral}}
{{Infobox mineral
| name = Cryolite
| category = Halide mineral
| boxwidth = 24
| boxbgcolor =
| image = 816- Ivigtut - cryolite.jpg
| imagesize = 260px
| caption = Cryolite from Ivittuut, Greenland
| formula = Na3AlF6
| molweight = 209.9 g mol−1
| strunz = 3.CB.15
| dana = 11.6.1.1
| system = Monoclinic
| class = Prismatic (2/m)
(same H-M symbol)
| symmetry = P21/n
| unit cell = a = 7.7564(3) Å,
b = 5.5959(2) Å,
c = 5.4024(2) Å; β = 90.18°; Z = 2
| color = Colorless to white, also brownish, reddish and rarely black
| habit = Usually massive, coarsely granular. The rare crystals are equant and pseudocubic
| lattice =
| twinning = Very common, often repeated or polysynthetic with simultaneous occurrence of several twin laws
| cleavage = None observed
| fracture = Uneven
| tenacity = Brittle
| mohs = 2.5 to 3
| luster = Vitreous to greasy, pearly on {001}
| refractive = nα = 1.3385–1.339, nβ = 1.3389–1.339, nγ = 1.3396–1.34
| opticalprop = Biaxial (+)
| birefringence = δ = 0.001
| dispersion = r < v
| 2V = 43°
| pleochroism =
| streak = White
| gravity = 2.95 to 3.0.
| melt = 1012 °C
| solubility = Soluble in AlCl3 solution, soluble in H2SO4 with the evolution of HF, which is poisonous. Insoluble in water.CRC Handbook of Chemistry and Physics, 83rd Ed., p. 4–84.
| diaphaneity = Transparent to translucent
| other = Weakly 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.
| references = {{cite book |last1=Gaines |first1=Richard V. |last2=Skinner |first2=H. Catherine W. |last3=Foord |first3=Eugene E. |last4=Mason |first4=Brian |last5=Rosensweig |first5=Abraham |title=Dana's new mineralogy : the system of mineralogy of James Dwight Dana and Edward Salisbury Dana. |date=1997 |publisher=Wiley |location=New York |isbn=978-0-471-19310-4 |edition=8th, entirely rewritten and greatly enl.}}{{cite web |url=http://www.mindat.org/min-1161.html |title=Cryolite: Cryolite mineral information and data |website=Mindat.org |date=3 October 2010 |access-date=25 October 2020}}{{cite web |url=http://www.webmineral.com/data/Cryolite.shtml |title=Cryolite Mineral Data |website=Webmineral.com. |access-date=25 October 2010}}{{cite web |url=http://rruff.geo.arizona.edu/doclib/hom/cryolite.pdf |title=Cryolite |website=Handbook of Mineralogy |access-date=25 October 2010}}{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. |title=Manual of mineralogy : (after James D. Dana) |date=1985 |publisher=Wiley |location=New York |isbn=0-471-80580-7 |edition=20th}}
}}
Cryolite (Na3AlF6, sodium hexafluoroaluminate) is a rare mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987.{{cite web |title=Eclipse Metals buys unique historical cryolite mine in Greenland |url=https://im-mining.com/2021/01/15/eclipse-metals-buys-unique-historical-cryolite-mine-greenland/ |website=im-mining.com |date=15 January 2021 |access-date=11 July 2022}}
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 {{ill|Peter Christian Abildgaard|da}} (1740–1801),{{cite journal |last=Abildgaard |year=1799 |title=Norwegische Titanerze und andre neue Fossilien |language=German |trans-title=Norwegian titanium ores and other new fossils [i.e., anything dug out of the earth]) |journal=Allgemeines Journal der Chemie |volume=2 |page=502 |url=https://books.google.com/books?id=d5YMAQAAIAAJ&pg=PA502 |quote=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.){{cite journal |last=Abildgaard |first=P. C. |year=1800 |title=Om Norske Titanertser og om en nye Steenart fra Grönland, som bestaaer af Flusspatsyre og Alunjord |language=Danish |trans-title=On Norwegian titanium ores and on a new mineral from Greenland, which consists of hydrofluoric acid and alumina |journal=Det Kongelige Danske Videnskabers-Selskabs (The Royal Danish Scientific Society) |series=3rd series |volume=1 |pages=305–316 |url=http://babel.hathitrust.org/cgi/pt?id=umn.31951d00004536u;view=1up;seq=333 |quote=[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.) 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.{{cite book | url=https://books.google.com/books?id=8Ynwkqa908oC&dq=Cryolite%20giesecke&pg=PA157 | title=The Mineral Collector | date=1903 | publisher=Mineral Collector Company }}{{cite book | url=https://books.google.com/books?id=oX4cAQAAMAAJ&dq=Cryolite%20Giesecke&pg=PA238 | title=Engineering and Mining Journal-press | date=1926 | publisher=McGraw-Hill Publishing Company }} 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:
- {{cite journal |last1=d'Andrada |title=Kurze Angabe der Eigenschaften und Kennzeichen einiger neuen Fossilien aus Schweden und Norwegen, nebst einigen chemischen Bemerkungen über dieselben |journal=Allgemeine Journal der Chemie |date=1800 |volume=4 |pages=28–39 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015066692545&view=1up&seq=32 |trans-title=Brief statement of the properties and characteristics of some new minerals from Sweden and Norway, together with some chemical observations about the same |language=German}} 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, … )
- Reprinted in French: {{cite journal |last1=d'Andrada |title=Des caractères et des propriétés de plusieurs nouveaux minéraux de Suède et de Norwège, avec quelques observations chimiques faites sur ces substances |journal=Journal de Physique, de Chimie, et d'Histoire Naturelle et des Arts |date=1800 |volume=51 |pages=239–246 |url=https://www.biodiversitylibrary.org/item/29658#page/251/mode/1up |trans-title=The characters and properties of several new minerals from Sweden and Norway, with some chemical observations on these substances |language=French}}
- Reprinted in English: {{cite journal |last1=d'Andrada |title=Short notice concerning the properties and external characters of some fossils from Sweden and Norway; together with some chemical remarks upon the same |journal=Journal of Natural Philosophy, Chemistry and the Arts |date=1802 |volume=5 |pages=193–196, 211–213 |url=https://www.biodiversitylibrary.org/item/20087#page/252/mode/1up}} See "Chryolite" on pp. 212–213. The name is derived from the Greek words {{lang|el-Latn|cryos}} ({{langx|el|κρύος|lit=frost}}), and {{lang|el-Latn|lithos}} ({{langx|el|λίθος|lit=stone|links=no}}).Albert Huntington Chester, A Dictionary of the Names of Minerals Including Their History and Etymology (New York, New York: John Wiley & Sons, 1896), [https://books.google.com/books?id=IiwFAAAAMAAJ&pg=PA68 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.{{Citation needed|date=January 2021}}
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.{{Citation needed|date=January 2021}}
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.{{Cite web |last=Magazine |first=Smithsonian |title=How This Abandoned Mining Town in Greenland Helped Win World War II |url=https://www.smithsonianmag.com/travel/how-abandoned-mining-town-greenland-helped-win-world-war-ii-180973835/ |access-date=2023-03-26 |website=Smithsonian Magazine |language=en}}
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,{{Cite journal |last=Sandré |first=Tanguy |date=3 March 2025 |title=Cryolite: le Danemark censure son histoire coloniale |url=https://blogs.mediapart.fr/tanguy-sandre/blog/030325/cryolite-le-danemark-censure-son-histoire-coloniale |journal=Mediapart}} though this claim has been strongly disputed.{{Cite web |last=Kajkus |first=Ines |last2=Lindberg |first2=Kristian |date=2025-02-10 |title=Vrede kilder beskylder DR for at manipulere seerne i sprængfarlig dokumentar: »Grebet ud af den blå luft« |url=https://www.berlingske.dk/kultur/vrede-kilder-beskylder-dr-for-at-manipulere-seerne-i-spraengfarlig |access-date=2025-04-01 |website=Berlingske.dk |language=da}}
Source locations
Image:Cryolite mine ivgtut greenland.jpg, Greenland, summer 1940]]
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.{{Cite web|title=Cryolite (Sodium Aluminum Fluoride)|url=http://www.galleries.com/Cryolite|access-date=2020-10-07|website=www.galleries.com}}{{Cite web|title=Cryolite {{!}} mineral|url=https://www.britannica.com/science/cryolite|access-date=2020-10-07|website=Encyclopedia Britannica|language=en}}
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{{cite journal |last1=Cassayre |first1=Laurent |last2=Palau |first2=Patrice |last3=Chamelot |first3=Pierre |last4=Massot |first4=Laurent |title=Properties of Low-Temperature Melting Electrolytes for the Aluminum Electrolysis Process: A Review |journal=Journal of Chemical & Engineering Data |date=11 November 2010 |volume=55 |issue=11 |pages=4549–4560 |doi=10.1021/je100214x|url=https://hal.archives-ouvertes.fr/hal-03474327/file/Cassayre_5793.pdf }} thus making the extraction of aluminium more economical.{{cite book |last1=Totten|first1=George E.|last2=MacKenzie|first2=D. Scott|date=2003|title= Handbook of Aluminum: Volume 2: Alloy production and materials manufacturing. vol. 2|location=New York, NY|publisher= Marcel Dekker, Inc.|isbn=0-8247-0896-2}}
Cryolite is used as an insecticide and a pesticide.{{cite journal |title=Efficacy of cryolite against major lepidopteran pests of cauliflower |last1=Rao |first1=J.R. |last2=Krishnayya |first2= P.V. |last3=Rao |first3=P.A. |journal=Plant Protection Bulletin |volume=52 |issue=3/4 |url=https://www.cabdirect.org/cabdirect/abstract/20013171514 |access-date=17 June 2021 |pages=16–18 |year=2000 |issn=0378-0449}} It is also used to give fireworks a yellow color.{{Cite web|url=https://www.thoughtco.com/chemistry-of-firework-colors-607341|title=How Firework Colors Work and the Chemicals That Make Vivid Colors|last=Helmenstine|first=Anne Marie|website=ThoughtCo|language=en|access-date=2019-09-01}}
It is used in glass manufacturing as a "powerful opaliser."{{cite journal |journal="Glass" (Industry Periodical) |title=The Chemical Calculation of Glass Compositions, p. 713 (March, 1925)|date=1924 |url=https://books.google.com/books?id=HZ0kAQAAMAAJ&dq=cryolite%20opaliser&pg=PA713}}
Physical properties
Image:Cryolite-unit-cell-3D-polyhedra.png. 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.
{{clear}}
References
{{Reflist}}
- [http://ammin.geoscienceworld.org/cgi/content/abstract/91/1/97 Phase transitions and volumetric properties of cryolite, Na3AlF6: Differential thermal analysis to 100 MPa; American Mineralogist; January 2006; v. 91; no. 1; p. 97-103]; {{doi|10.2138/am.2006.1772}}
{{Authority control}}
Category:Natural history of Greenland
Category:Pyrotechnic colorants
Category:Minerals in space group 14