Peridotite
A coarse-grained, ultrabasic, igneous rock consisting of essential magnesium-rich olivine accompanied by lesser amounts of other ferromagnesian minerals, e.g. orthopyroxene (enstatite-bronzite), clinopyroxene (chromium-diopside), and chromite, with or without pyrope garnet. Peridotites are found in large, layered, ultrabasic, intrusive bodies, in ophiolite complexes, and as xenoliths brought up in alkali basalts and kimberlites. As well as forming by crystal fractionation processes in igneous bodies, their mineral chemistry and presence as xenoliths in kimberlites suggest that much of the Earth's mantle, and therefore of the mass of the Earth, is peridotite. Meteorites are also composed largely of peridotite, suggesting that peridotites are probably the commonest rock in the solar system. — A Dictionary of Geology and Earth Sciences (4 ed.), Oxford University Press
