Cryolite
Cryolite is a very gem that is rare gem quality crystals have become rare and only available from a single source. Its typically colorless and usually has an appearance that is somewhat sleepy. The index of refraction of Cryolite is 1.3385, that is very near to your index of refraction of water (1.3328). The result is that it will basically disappear if you put a clean, colorless gem or crystal of Cryolite in water.
Resources of Cryolite consist of the Ivigtut section of Greenland and also at the base of Pikes Peak at Creede, Colorado, USA, Mont Saint-Hilaire and Francon Quarry, Montreal, Quebec, Canada as well as Minsk, Russia. Gem quality crystals are usually only from Francon Quarry.
| Category: | Halide Mineral |
| Formula: | Na3•AlF6 |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals are pseudocubic or short prismatic, striated, to 3 cm; also typically massive or coarsely granular. |
| Twinning: | Common, according to one or more of 13 distinct twin laws, producing penetration, repeated, or polysynthetic twins |
| Cleavage: | None; Parting on [001] and [110] |
| Fracture: | Irregular, Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 2.5 – 3.0 |
| Density: | 2.95 – 3.00 (g/cm3) |
| Luminescence: | Weakly thermoluminescent; may fluoresce intense yellow under SW UV, with yellow phosphorescence, pale yellow fluorescence under LW UV. |
| Radioactivity: | Not Radioactive |
| Other: | Slightly soluble in water |
| Color: | Colorless, Gray, White, Reddish brown, Brownish black |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous, Greasy, Pearly |
| Refractive Index: | 1.3385 – 1.340 Biaxial ( + ) |
| Birefringence: | 0.0010 – 0.0011 |
| Dispersion: | None; r < v |
| Pleochroism: | X = colorless; Y = colorless; Z = colorless |
