igneous
Peridotite
Ultramafic intrusive igneous rock (composition: (Mg, Fe)2SiO4)
Hardness: 6.5-7 Mohs; Color: Olive green to dark green with brown iron-oxide staining; Luster: Vitreous to dull; Crystal structure: Orthorhombic (specifically Olivine grains); Cleavage: Poor/indistinct; Specific Gravity: 3.2-3.4
- Hardness
- 6
- Color
- Olive green to dark green with brown iron-oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Olive green to dark green with brown iron-oxide staining; Luster: Vitreous to dull; Crystal structure: Orthorhombic (specifically Olivine grains); Cleavage: Poor/indistinct; Specific Gravity: 3.2-3.4
Formation & geological history
Formed deep in the upper mantle of the Earth via slow cooling of ultramafic magma. It is typically brought to the surface through tectonic processes or volcanic pipes. Most specimens date back to the Precambrian or Paleozoic eras.
Uses & applications
Peridotite is the primary source of the gemstone peridot. Industrially, it is being researched as a medium for carbon sequestration (absorbing CO2). It is also used as a decorative stone and a source of magnesium and chromium.
Geological facts
Peridotite is the dominant rock type of Earth's upper mantle. Some peridotite specimens contain diamonds if they originated from high-pressure depths. It often undergoes hydration to become serpentinite.
Field identification & locations
Identify by its distinctive olive-green color and coarse crystalline texture. It is heavy for its size. It is commonly found in ophiolites (sections of oceanic crust obducted onto land) and in kimberlite pipes. Use a hand lens to look for translucent green olivine grains.
