Sinhalite
Sinhalite is a very rare gem that was long thought to be a brown variety of Peridot but in 1952 an investigation determined it to be a new mineral. It has weak pleochroism from pale brown to yellow to greenish brown. The most notable occurances of Sinhalite are from the gem gravels of Sri Lanka in the Ratnapura district, at Nivitigala, Balangoda, Nirialla; around Elahera and Eheliyagoda; and elsewhere. Also from Mogok, Myanmar, in gem gravels. Non-gem quality material can be found at a few other locations around the world.
| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Most occurances are found as rolled pebbles in gem gravels. Rarely found as euhedral crystals, equant to prismatic, to 2 cm; anhedral grains. |
| Twinning: | None |
| Cleavage: | Indistinct |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.5 – 7.0 |
| Density: | 3.47 – 3.50 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Colorless, pale yellow, yellow, greenish brown, dark brown; brownish pink, pale pink if chromian |
| Transparency: | Transparent |
| Luster: | Vitreous (glassy) |
| Refractive Index: | 1.667 – 1.712 Biaxial ( – ) |
| Birefringence: | 0.035 – 0.037 |
| Dispersion: | Strong; r > v |
| Pleochroism: | Weak; X = brown, pale yellow; Y = green, pale brown, bluish gray; Z = paler brown, pale greenish brown, pale pinkish gray |
