An ultramafic igneous rock composed of at least 90% olivine. Important accessory minerals (abundances usually less than 1%) found in different occurrences of dunite include chromian spinel, low- or high-calcium pyroxenes (enstatite and diopside), and plagioclase. If these minerals constitute greater than 10% of the rock, it is called chromitite, peridotite, or troctolite, respectively. Low-temperature alteration (less than 750°F or 400°C) causes hydration of olivine to the mineral serpentine and, where extensive, may transform dunite to the metamorphic rock serpentinite. Dunite was first described at Dun Mountain, New Zealand. The dun color is a characteristic feature of the weathered rock.