Peridotite (US: /ˈpɛrɪdoʊˌtaɪt, pəˈrɪdə-/ PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene.

The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole.

Peridotitic outcrops typically range from earthy bright yellow to dark green; this is because olivine is easily weathered to iddingsite.

Igneous rocks rich in magnesium and iron with a color index greater than 90 are defined as ultramafic.

[21] This distinction is important in the classification of pyroxene peridotites[4][5] since clinopyroxene melts more easily than orthopyroxene or olivine.

[21] Hornblende is an amphibole, a group of minerals resembling pyroxenes but with a double chain structure incorporating water.

However, pieces can be emplaced into or overthrust on continental crust by a process called obduction, rather than carried down into the mantle.

Typical ophiolites consist mostly of peridotite plus associated rocks such as gabbro, pillow basalt, diabase sill-and-dike complexes, and red chert.

Peridotite xenoliths contain osmium and other elements whose stable isotope ratios provide clues on the formation and evolution of the Earth's mantle.

[37] The volcanic equivalent of peridotites are komatiites, which were mostly erupted early in the Earth's history and are rare in rocks younger than Archean in age.

Many, if not most, surface outcrops have been at least partly altered to serpentinite, a process in which the pyroxenes and olivines are converted to green serpentine.

[20] This hydration reaction involves considerable increase in volume with concurrent deformation of the original textures.

[41] Distinctive plant communities grow in soils developed on serpentinite, because of the unusual composition of the underlying rock.

[57] Peridotites associated with Alaskan-type ultramafic complexes are cumulates that probably formed in the root zones of volcanoes.

[60] Eclogite is a metamorphic rock composed primarily of omphacite (sodic clinopyroxene) and pyrope-rich garnet.

[62] Peridotite may potentially be used in a low-cost, safe and permanent method of capturing and storing atmospheric CO2 as part of climate change-related greenhouse gas sequestration.

[66] Peridotite that has been hydrated at low temperatures is the protolith for serpentinite, which may include chrysotile asbestos (a form of serpentine)[43] and talc.

Sulfides associated with peridotites form nickel ores and platinoid metals; most of the platinum used in the world today is mined from the Bushveld Igneous Complex in South Africa and the Great Dyke of Zimbabwe.