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 February 25, 2026More igneous →

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Physical properties

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.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral