DUNITE

light yellowish green, intrusive igneous rock that is composed almost entirely of olivine. Dunite usually forms sills (tabular bodies intruded between other rocks) but may also occur as lenses (thin-edged strata) or pipes (funnels, more or less oval in cross section, that become narrower with increasing depth). Occurrences include Dun Mountain, New Zealand, from which the rock takes its name; the Bushveld Igneous Complex, South Africa; and Frostviken, Jmtland, Sweden. Chromite, picotite, and magnetite also occur in dunite, as do spinel, ilmenite, pyrrhotite, and platinum in some cases. Dunites constitute an important source of chromium, a commercially valuable metal.