Peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron.


Peridotite is derived either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole. The compositions of peridotite nodules preserve isotope ratios of osmium and other elements that record processes over three billion years ago, and so they are of special interest to paleogeologists because they provide clues to the composition of the early mantle and the complexities of the processes that were involved.

The word peridotite comes from the gemstone peridot, which consists of pale green olivine.

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