Sillimanite
Mineral Al2SiO5
Also called Fibrolite
About it
Long slender prisms and silky fibrous mats in high-grade schist and gneiss; the high-temperature form of Al2SiO5. Fibrous fibrolite is cut into cabochons.
- Type
- Mineral
- Group
- Silicate (nesosilicate), sillimanite group
- Formula
- Al2SiO5
- Hardness (Mohs)
- 6.5–7.5
- Specific gravity
- 3.23–3.27
- Streak
- white
- Lustre
- vitreous (glassy), silky
- Crystal system
- Orthorhombic
- Colours
- white, grey, brown, green, colourless
- Transparency
- transparent, translucent
- Cleavage and fracture
- perfect in one direction
Typical values: real specimens vary. For more, see mindat.org.