Cryolite

Cryolite
Cryolite
	Cryolite from Ivittuut, Greenland
General
Category	Halide mineral
Formula; (repeating unit)	Na3AlF6
IMA symbol	Crl
Strunz classification	3.CB.15
Dana classification	11.6.1.1
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) ; (same H-M symbol)
Space group	P21/n
Unit cell	a = 7.7564(3) Å, ; b = 5.5959(2) Å, ; c = 5.4024(2) Å; β = 90.18°; Z = 2
Identification
Formula mass	209.9 g mol−1
Color	Colorless to white, also brownish, reddish and rarely black
Crystal habit	Usually massive, coarsely granular. The rare crystals are equant and pseudocubic
Twinning	Very common, often repeated or polysynthetic with simultaneous occurrence of several twin laws
Cleavage	None observed
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	2.5 to 3
Luster	Vitreous to greasy, pearly on {001}
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.95 to 3.0.
Optical properties	Biaxial (+)
Refractive index	nα = 1.3385–1.339, nβ = 1.3389–1.339, nγ = 1.3396–1.34
Birefringence	δ = 0.001
2V angle	43°
Dispersion	r < v
Melting point	1012 °C
Solubility	Soluble in AlCl3 solution, soluble in H2SO4 with the evolution of HF, which is poisonous. Insoluble in water.
Other characteristics	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

Cryolite (Na₃Al F₆, sodium hexafluoroaluminate) is an uncommon mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987.^[8]

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

^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
^ CRC Handbook of Chemistry and Physics, 83rd Ed., p. 4–84.
^ Gaines, Richard V.; Skinner, H. Catherine W.; Foord, Eugene E.; Mason, Brian; Rosensweig, Abraham (1997). Dana's new mineralogy : the system of mineralogy of James Dwight Dana and Edward Salisbury Dana (8th, entirely rewritten and greatly enl. ed.). New York: Wiley. ISBN 978-0-471-19310-4.
^ "Cryolite: Cryolite mineral information and data". Mindat.org. 3 October 2010. Retrieved 25 October 2020.
^ "Cryolite Mineral Data". Webmineral.com. Retrieved 25 October 2010.
^ "Cryolite" (PDF). Handbook of Mineralogy. Retrieved 25 October 2010.
^ Klein, Cornelis; Hurlbut, Cornelius S. (1985). Manual of mineralogy : (after James D. Dana) (20th ed.). New York: Wiley. ISBN 0-471-80580-7.
^ "Eclipse Metals buys unique historical cryolite mine in Greenland". im-mining.com. Retrieved 11 July 2022.