Diamonds are generally either eclogitic or peridotitic. Peridotitic diamonds are found crystalized in peridotitic source rocks. Peridotites are enriched in chrome and are dominantly composed of olivine, orthopyroxene, clinopyroxene, chromite and pyrope garnet.
A coarse-grained plutonic rock composed chiefly of olivine with or without other mafic minerals, such as pyroxenes, amphiboles, or micas, and containing little or no feldspar. Peridotite is commonly altered to serpentinite.
Peridotite is a dense, coarse-grained rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic and ultrabasic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron.