Forsterite (Mg₂SiO₄) is the magnesium end-member of the olivine group and one of the most abundant minerals in Earth’s upper mantle. The gem variety peridot supplies the August birthstone. Forsterite is a diagnostic kimberlite indicator mineral — co-occurring with pyrope garnet and ilmenite as evidence of mantle-sourced magma at diamond-bearing localities like Mengyin (Shandong) and Wafangdian (Liaoning).
Key Facts
- Mohs hardness 6.5–7.
- Orthorhombic; forms a continuous solid-solution series with fayalite (Fe₂SiO₄).
- Peridot variety is the gem-quality olive-green form (Fe-bearing).
- Diagnostic mantle / kimberlite indicator mineral.
- Major component of basalt, peridotite, and dunite host rocks.
Notable Localities
Zabargad Island (Egypt) and Pakistan supply gem peridot. San Carlos Apache Reservation (Arizona) yields massive olivine. Mengyin (Shandong) and Wafangdian (Liaoning) host kimberlite forsterite.
Found at these Localities
- Mogok Stone Tract (抹谷宝石产地)
- Wafangdian Diamond Mine (瓦房店金刚石矿)
- Mengyin Diamond Mine (蒙阴金刚石矿)
