igneous
Peridotite
Peridotite (varieties include Dunite, Lherzolite, Harzburgite)
Hardness: 6.5-7 (Mohs scale); Color: Olive-green to dark green; Luster: Vitreous to greasy; Crystal Structure: Orthorhombic; Specific Gravity: 3.2-3.4; Cleavage: Poor/Imperfect. Dominantly composed of Olivine and Pyroxene.
- Hardness
- 6
- Color
- Olive-green to dark green
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Olive-green to dark green; Luster: Vitreous to greasy; Crystal Structure: Orthorhombic; Specific Gravity: 3.2-3.4; Cleavage: Poor/Imperfect. Dominantly composed of Olivine and Pyroxene.
Formation & geological history
Formed in the Earth's mantle through slow cooling of ultramafic magma. They are brought to the surface via tectonic processes (Ophiolites) or volcanic eruptions (Xenoliths). Most are Archean to Proterozoic in mantle age.
Uses & applications
Primary source of chromium ore (chromite). Used as a gemstone (Peridot) and as an industrial material for capturing and storing carbon dioxide (CO2 sequestration).
Geological facts
Peridotite is the dominant rock of the Earth's upper mantle down to depths of 400 km. It is extremely rare to find large outcrops on the Earth's crust surface because it is chemically unstable at the surface and easily weathers into serpentine.
Field identification & locations
Identify by the characteristic olive-green color and heavy weight compared to other rocks. Found in mountain belts like the Alps or via volcanic inclusions in basalt. Collectors look for bright green olivine crystals (Peridot).
