Dunite is an igneous intusive rock which is a coarsed grained, greenish colour. It is composed of mineral olivine up to 90 percent. Some dunites are rich in chromite, magnetite, ilmenite or pyrrhotite and can also have small amount of pyroxene. Dunite occurs in layered gabbroic complexes. It probably forms from the accumulation of dense, early crystallizing grains of olivine that sink to the bottom of low silica magma. Intrusions of dunite form sills or dikes. Some dunite has been altered to form serpentine. Dunite is named after Dun mountain in New Zealand.