Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
Cut cryolite is somewhat translucent, and has a “sleepy” look. The cuttable material has a very low birefringence, is colorless, and very soft—not exactly an exciting-looking gem. However, there are very few cut stones in existence because of the extreme scarcity of suitable rough. In addition, cryolite is only found abundantly at one locality (Ivigtut).
| Data | Value |
|---|---|
| Name | Cryolite |
| Colors | Colorless, white, brownish, reddish; rarely gray to black. |
| Hardness | 2.5 |
| Fracture | Uneven |
| Cleavage | None |
| Stone Sizes | Large cabochons could be cut from the abundant material in Greenland. Facetable material is quite rare, however, and only tiny gems can be obtained. |
| Formula | Na3AlF6. |
| Crystallography | Monoclinic. Crystals cuboidal and prismatic; usually massive. |
| Refractive Index | 1.338-1.339 |
| Birefringence | 0.001; almost isotropic. |
| Dispersion | 0.024 (approximately) |
| Luminescence | None observed. |
| Luminescence Present | No |
| Absorption Spectrum | Not diagnostic. |
| Pleochroism | None |
| Optics | a = 1.338; β = 1.338; γ = 1.339. Biaxial (+), 2V = 43°. |
| Optic Sign | Biaxial + |
| Luster | Vitreous to greasy. |
| Specific Gravity | 2.97 |
| Transparency | Translucent. |
Optics: a = 1.338; β = 1.338; γ = 1.339.
Biaxial (+), 2V= 43°.
Occurrence: Occurs in alkalic rocks at Ivigtut, Greenland.
Also Spain; USSR; Colorado (small amounts).
Comments: Cut cryolite is somewhat translucent, and has a “sleepy” look. The cuttable material has a very low birefringence, is colorless, and very soft—not exactly an exciting-looking gem. However, there are very few cut stones in existence because of the extreme scarcity of suitable rough. In addition, cryolite is only found abundantly at one locality (Ivigtut).
Name: From the Greek kryos (frost) and lithos (stone), hence ice-stone, in allusion to its appearance.
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