igneous
Peridotite (with Olivine and Pyroxene)
Ultramafic Magmatic Rock (Primary minerals: (Mg, Fe)2SiO4 and (Ca, Mg, Fe)2Si2O6)
Hardness: 6.5 to 7 on Mohs scale; Color: Dark green to blackish-green with olive-green translucent crystals (olivine); Luster: Vitreous to dull; Crystal structure: Orthorhombic/Monoclinic; Cleavage: Poor/None; Specific Gravity: 3.2 to 3.4.
- Hardness
- 6
- Luster
- Vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6.5 to 7 on Mohs scale; Color: Dark green to blackish-green with olive-green translucent crystals (olivine); Luster: Vitreous to dull; Crystal structure: Orthorhombic/Monoclinic; Cleavage: Poor/None; Specific Gravity: 3.2 to 3.4.
Formation & geological history
Formed in the Earth's mantle through the slow cooling of ultramafic magma. They are often transported to the surface by tectonic activity or volcanic eruptions as xenoliths. Most specimens represent ancient mantle material, often billions of years old.
Uses & applications
Primary source of magnesium and chromium ores. Certain varieties (dunite) are used in steelmaking as flux. High-quality olivine crystals are harvested as the gemstone 'Peridot'. It is also used in carbon sequestration research.
Geological facts
Peridotite is the dominant rock type of the Earth's upper mantle. It is rarely seen on the surface because it is unstable at low pressures and easily hydrates into serpentinite. It is also found in stony-iron meteorites (pallasites).
Field identification & locations
Identify in the field by its high density, dark green color, and granular texture. Often found in ophiolite complexes (ancient ocean floor pushed onto land) or as heavy nodules in basalt flows. Common locations include the Red Sea, Norway, and Arizona.
