igneous
Peridotite
Ultramafic intrusive igneous rock
Hardness varies by mineral content (6-7 on Mohs scale), typically dark green to brownish-green in color, dull to sub-vitreous luster, granular crystal structure with coarse-grained texture, and specific gravity around 3.2-3.4.
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Physical properties
Hardness varies by mineral content (6-7 on Mohs scale), typically dark green to brownish-green in color, dull to sub-vitreous luster, granular crystal structure with coarse-grained texture, and specific gravity around 3.2-3.4.
Formation & geological history
Formed from the slow cooling and crystallization of magnesium- and iron-rich silicate magma deep within the Earth's mantle, or as accumulations of olivine and pyroxene crystals at the base of layered mafic intrusions.
Uses & applications
Primarily of geological and scientific interest as the dominant rock type of the Earth's upper mantle; source rock for gemstones such as peridot and chromium deposits; sometimes used in carbon sequestration research.
Geological facts
Peridotite is exceptionally dense and rich in olivine. When subjected to high pressures and temperatures near the Earth's surface, it can undergo serpentinization, turning into serpentinite.
Field identification & locations
Identified in the field by its dark, greenish-gray, coarse-grained appearance and heavy weight relative to its size. Commonly found in ophiolite sequences, mountain-building belts, and xenoliths brought up by volcanic eruptions.
