Fayalite
| Fayalite | |
|---|---|
| General | |
| Category | Mineral |
| Chemical formula | Iron silicate (Fe2SiO4) |
| Identification | |
| Colour | Pale yellow, amber and green |
| Crystal system | Orthorhombic |
| Cleavage | {010} moderate, {100} week |
| Fracture | Conchoidal |
| Mohs Scale hardness | 6.5 |
| Luster | Vitreous |
| Refractive index | α = 1.827, β = 1.869, γ = 1.879 |
| Specific gravity | 4.392 |
Fayalite (Fe2SiO4) is the iron rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a 4.82 Å, b 10.48 Å and c Å 6.09.
Iron rich olivine is a relatively common constituent of acidic and alkaline igneous rocks such as volcanic obsidians, rhyolites, trachytes and phonolites and plutonic quartz syenites where it is associated with amphiboles. It also occurs in medium-grade thermally metamorphosed iron-rich sediments.
References
- Deer, W. A., Howie, R. A., and Zussman, J. (1992). An introduction to the rock-forming minerals (2nd ed.). Harlow: Longman ISBN 0-582-30094-0