Peridotiet

Peridotiet, or peridotite in English, is a group of ultramafic, coarse-grained igneous rocks dominated by the minerals olivine and pyroxene. The common varieties include dunite (mostly olivine), harzburgite (olivine with orthopyroxene and little clinopyroxene), and lherzolite (olivine, orthopyroxene, and clinopyroxene). Accessory minerals such as chromian spinel or garnet may be present. The name reflects a greenish hue in parts, connected to the gemstone peridot, which is the gem form of olivine; however peridotite itself is not a gemstone.

Formation and occurrence: Peridotite forms in the Earth's mantle and is typically brought to the surface as mantle xenoliths embedded in magmas such as kimberlites and alkali basalts. It also occurs in ophiolites, where sections of oceanic mantle are emplaced onto continental crust. These rocks provide direct samples of upper mantle composition and processes.

Geochemistry and significance: Peridotite is ultramafic, with low silica and high magnesium and iron contents. Its mineralogy records mantle melting and melt extraction, giving insight into mantle convection, chemical differentiation, and the boundaries between mantle zones. The study of peridotite and its xenoliths helps elucidate the structure and evolution of the Earth's mantle and crust formation.

Economic context: Peridotite itself is not a major ore resource, but its mantle-derived rocks are central to petrological research and to understanding mantle dynamics. Related terms include olivine, pyroxene, ultramafic rocks, kimberlite, and ophiolite.