Peridotit

Peridotite is a group of dense, ultramafic rocks that originate in the Earth’s mantle. It is dominated by the mineral olivine and one or more pyroxenes, and it is the primary rock type sampled in mantle xenoliths and exposed in ophiolite complexes. The best-known varieties are dunite (mostly olivine), harzburgite (olivine and orthopyroxene), and lherzolite (olivine, orthopyroxene, and clinopyroxene).

In mineralogy, peridotite commonly contains accessory minerals such as chromian spinel, magnetite or ilmenite, and sometimes garnet in the high-pressure portion of the mantle. Serpentinized peridotite, formed when mantle rocks react with water, is called serpentinite and is common in subduction and fault zones. The rock’s high magnesium and iron content give it very high density and low silica.

Origins and significance: peridotite forms primarily by partial melting of mantle rocks, with melt removal leaving a depleted, mantle-derived residue. It is a key reference rock for studying mantle composition, structure, and geodynamic processes, including plate tectonics and mantle convection. Mantle peridotites are preserved as xenoliths carried by magmas to the surface and in ancient ophiolites that expose oceanic lithosphere.

Distribution and occurrence: peridotite is found in many tectonic settings, including ophiolites, continental ophiolite belts, and large mantle diapirs. Its study provides insights into the composition of the upper mantle and the conditions under which magmas originate and evolve.