Sillimanite
| Colour | Gray, White, Brown |
|---|---|
| Mohs hardness | 7 |
| Lustre | Vitreous to subadamantine, silky |
| Streak | White |
| Crystal system | Orthorhombic |
| Transparency | Transparent to translucent |
| Cleavage | {010} perfect |
| Fracture | Splintery |
| Chemical formula | Al 2 SiO 5 |
| Specific gravity | 3.24 |
What is Sillimanite?
Sillimanite or fibrolite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Connecticut.
How to identify Sillimanite
- Lustre: Vitreous to subadamantine, silky.
- Hardness: Mohs 7 — hard enough to scratch glass.
- Streak: White.
- Habit: Orthorhombic crystal system.
Sillimanite in different forms
Stones often confused with Sillimanite
Frequently asked questions
How hard is Sillimanite?
Sillimanite is Mohs 7 on the hardness scale.
What colour is Sillimanite?
Sillimanite is typically gray, white, brown (Colourless or white to grey, also brown, yellow, yellow-green, grey-green, blue-green, blue; colourless in thin section).