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| Cryolite | |
|---|---|
 Cryolite from Ivittuut, Greenland | |
| General | |
| Category | Halide mineral |
| Formula (repeating unit) | Na3AlF6 |
| IMA symbol | Crl[1] |
| 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.[2] |
| 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 | [3][4][5][6][7] |
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.[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. 15 January 2021. Retrieved 11 July 2022.