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