Igneous
Peridotite
Ultramafic intrusive rock (Peridotite)
Hardness: 6.5–7 (Mohs scale); Color: Olive-green, dark green to black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained), typically granular; Specific gravity: 3.2–3.4; Composition: Principally olivine and pyroxene.
- Hardness
- 6
- Color
- Olive-green, dark green to black
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Olive-green, dark green to black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained), typically granular; Specific gravity: 3.2–3.4; Composition: Principally olivine and pyroxene.
Formation & geological history
Formed by the slow cooling of ultramafic magma deep within the Earth's mantle or at the base of the crust. It is a primary constituent of the Earth's upper mantle and can be uplifted during tectonic events or as xenoliths in volcanic eruptions.
Uses & applications
Primary source of magnesium and chromium ores (chromite). In construction, it is used as crushed stone for road bases. Large, gem-grade olivine crystals from peridotite are known as Peridot and used in jewelry.
Geological facts
Peridotite is thought to be the most abundant rock type in the Earth's upper mantle. It is often scientifically studied to understand the composition of the deep Earth and the process of mantle convection.
Field identification & locations
Identify in the field by its distinct dark olive-green color and coarse-grained, 'sugary' texture. Locations include ophiolite complexes (e.g., Oman, Cyprus) and mantle xenoliths in basalt flows. Collectors look for bright green olivine phenocrysts.
