An ultramafic plutonic rock composed primarily of
the mineral olivine. It may have less than 10 percent orthopyroxene,
clinopyroxene, hornblende, chromite, and other
minor constituents. Most dunites are cumulates formed by
the settling of dense olivine crystals in a peridotitic melt.
They are commonly found in cumulate sequences in ophiolites,
from the bases of island arcs, and in continental intrusions.
The rock is named after Dun Mountain in New
Zealand, where it was first recognized by Ferdinand von
Hochstetter in 1864.
See also IGNEOUS ROCKS; ISLAND ARC; OPHIOLITES.
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