Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
Sellaite
An overview on Sellaite Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of Sellaite gems.
Sellaite Information
| Data | Value |
|---|---|
| Name | Sellaite |
| Crystallography | Tetragonal: crystals prismatic, acicular, fibrous aggregates. |
| Refractive Index | 1.378-1.390 |
| Colors | Colorless, white. |
| Hardness | 5-5.5 |
| Fracture | Conchoidal |
| Birefringence | 0.012 |
| Cleavage | Poorly observed although literature indicates perfect in 2 directions |
| Stone Sizes | The Brazilian sellaite is the world‘s only extant cuttable material, and the largest crystals found thus far are only 5 cm long with small transparent areas. Thus, gems of only a few carats have or could be produced. This is an exceedingly rare gemstone, both in occurrence and number of cut stones. |
| Luminescence | None reported. |
| Luminescence Present | No |
| Absorption Spectrum | None. |
| Formula | MgF2. |
| Pleochroism | None. |
| Optics | o = 1.378; e = 1.390. Uniaxial (+). |
| Optic Sign | Uniaxial + |
| Luster | Vitreous. |
| Specific Gravity | 3.15 |
| Transparency | Transparent. |
Optics: o=1.378; e= 1.390.
Uniaxial (+).
Occurrence: Sellaite occurs in a wide variety of geological environments.
Vesuvius, Italy: in volcanic fumaroles.
Harz Mountains, Germany: in evaporite beds.
Italy; France: in veins.
Nertschin, Russia: in pegmatites.
Oslo Region, Norway: cavities in a soda-granite.
Brumado Mine, Bahia, Brazil: gemmy crystals in a metamorphic magnesite deposit.
Name: After the Italian mining engineer and mineralogist, Quintino Sella.
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