Fayalite
Mineral Fe2SiO4
About it
The iron olivine, brown to black and much heavier than forsterite; in cavities in obsidian and rhyolite, as at Obsidian Cliff, Yellowstone, and in granite and slag.
- Type
- Mineral
- Group
- Silicate (nesosilicate), olivine group
- Formula
- Fe2SiO4
- Hardness (Mohs)
- 6.5
- Specific gravity
- 4.3–4.4
- Streak
- white
- Lustre
- vitreous (glassy), resinous
- Crystal system
- Orthorhombic
- Colours
- yellow, brown, black, greenish yellow
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- poor; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.