igneous
Peridotite (Dunite/Peridot Xenolith)
Peridotite (predominantly Olivine (Mg, Fe)2SiO4)
Hardness: 6.5-7 (Olivine); Color: Olive-green to yellowish-green; Luster: Vitreous to dull; Crystal structure: Orthorhombic; Specific Gravity: 3.2-3.4. Features a coarse-grained, phaneritic texture of interlocking olivine crystals.
- Hardness
- 6
- Color
- Olive-green to yellowish-green
- Luster
- Vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6.5-7 (Olivine); Color: Olive-green to yellowish-green; Luster: Vitreous to dull; Crystal structure: Orthorhombic; Specific Gravity: 3.2-3.4. Features a coarse-grained, phaneritic texture of interlocking olivine crystals.
Formation & geological history
Formed in the Earth's upper mantle through fractional crystallization. These specimens are often brought to the surface as xenoliths (foreign rocks) within basaltic lava flows during volcanic eruptions. Most are extremely old, dating back millions to billions of years.
Uses & applications
Primarily of scientific interest for studying the mantle; used as a source for the gemstone peridot; industrially used in the sequestration of CO2 and as refractory material.
Geological facts
Peridotite is the dominant rock of the upper part of Earth's mantle. When it contains over 90% olivine, it is specifically called Dunite. It is rare at the Earth's surface because it is unstable at low pressures and easily hydrates into serpentinite.
Field identification & locations
Identify by its distinctive olive-green color and granular 'sugary' texture. Commonly found in volcanic areas like San Carlos, Arizona, or in ophiolite complexes. Collectors look for high clarity olivine crystals within the matrix.
