Peridotite

Peridotite, igneous rock composed of pyroxene, olivine, and hornblende. It is the rock that makes up the earth's mantle. Magnetite, chromite, ilmenite, and garnet are often associated with peridotite. Various types of peridotite are pyroxenite, a variety composed almost entirely of pyroxene; hornblendite, a rare variety composed almost entirely of hornblende; serpentine, a variety composed almost entirely of olivine that has altered completely; and kimberlite, a variety containing diamond. Peridotite is the most important source of chromium.