Sogdianite
Sogdianite is an extremely rare gem. There are only three known sources: the Dara-i-Pioz massif, Alai Range, Tien Shan, Tajikistan; the Wessels mine, near Kuruman, Cape Province, South Africa; at Washington Pass, Okanogan Co., Washington, USA. Sogdianite is often mixed with other minerals so the specific gravity and hardness are variable. It is closely related to Sugilite.
| Crystallography: | Hexagonal – Dihexagonal Dipyramidal |
| Crystal Habit: | Crystals are Tabular, to 1 cm; in platy aggregates, to 15 cm. |
| Twinning: | None |
| Cleavage: | [0001] Perfect |
| Fracture: | Sub-Conchoidal to Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 5.0 – 7.0 (7.0 if pure) |
| Density: | 2.76 – 2.90 (g/cm3) (2.90 if pure) |
| Luminescence: | Fluoresces dark violet under LW UV and very dark red under SW UV. |
| Radioactivity: | Barely Detectable, GRapi = 79.14 (Gamma Ray American Petroleum Institute Units) |
| Color: | Violet |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous to Waxy |
| Refractive Index: | 1.606 – 1.608 Uniaxial ( – ) |
| Birefringence: | 0.0020 |
| Dispersion: | n/a |
| Pleochroism: | None |
