igneous
Peridotite
Peridotite (composed largely of Olivine (Mg,Fe)2SiO4 and Pyroxene)
Hardness: 6.5-7 (Mohs); Color: Dark green to blackish-green; Luster: Vitreous to oily; Crystal structure: Orthorhombic (olivine crystals); Specific gravity: 3.2-3.4
- Hardness
- 6
- Color
- Dark green to blackish-green
- Luster
- Vitreous to oily
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Dark green to blackish-green; Luster: Vitreous to oily; Crystal structure: Orthorhombic (olivine crystals); Specific gravity: 3.2-3.4
Formation & geological history
Ultramafic intrusive igneous rock formed in the Earth's mantle or via crystal settling in magma chambers. Most specimens are extremely old, often billions of years, brought to the surface through tectonic uplift or volcanic activity.
Uses & applications
Primary source of the gemstone peridot; used as a flux in steel making, and as a decorative stone for indoor/outdoor landscaping. Crucial for understanding the composition of the Earth's mantle.
Geological facts
Peridotite is the dominant rock type of the upper mantle. Rare specimens can be found that contain diamonds or platinum-group elements. It is also an active candidate for carbon sequestration research.
Field identification & locations
Identified by its high density and dark olive-green granular appearance. Commonly found in ophiolites (fragments of oceanic crust pushed onto land) and as nodules inside basaltic lavas.
