igneous
Peridotite (with Olivine)
Peridotite (rich in Olivine, (Mg,Fe)2SiO4)
Hardness: 6.5-7 (olivine); Color: Olive-green to lime-green crystals in a dark grey or black matrix; Luster: Vitreous to oily; Crystal structure: Orthorhombic; Specific Gravity: 3.2-3.4.
- Hardness
- 6
- Luster
- Vitreous to oily
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Physical properties
Hardness: 6.5-7 (olivine); Color: Olive-green to lime-green crystals in a dark grey or black matrix; Luster: Vitreous to oily; Crystal structure: Orthorhombic; Specific Gravity: 3.2-3.4.
Formation & geological history
Formed deep within the Earth's mantle through fractional crystallization of magma. These specimens are often brought to the surface as xenoliths inside basaltic lava flows during volcanic eruptions.
Uses & applications
Primary source of the gemstone Peridot; used in industrial refractory processes due to high melting points; significant for geological research on mantle composition.
Geological facts
Peridotite is the dominant rock of the upper part of Earth's mantle. Common green olivine crystals found within it are often called 'Hawaiian diamonds' when found in volcanic sands.
Field identification & locations
Identify in the field by looking for distinct yellowish-green glassy crystals embedded within dark, heavy, fine-grained volcanic rock (basalt). Common in volcanic regions like Hawaii, Arizona, and the Canary Islands.
