A rock of ultramafic composition, dunite contains less than 45 percent total silica and no quartz. It is made up almost entirely of olivine, which gives the rock its recognizable greenish or brownish coloring. The alternative name, olivinite, refers to its mineral composition. Chromite occurs in this rock as an accessory mineral.

TEXTURE A medium-grained rock with crystals 1⁄64–3⁄16 in (0.5–5 mm) in diameter. The texture of dunite is granular and sugary.

ORIGIN Small volumes of ultramafic rocks are often formed as cumulates during the differentiation of mafic rocks in a plutonic environment.
Minerals in some dunites are sometimes crushed, and they may be emplaced in a near-solid state due to Earth movements. This can produce a mass of ultramafic rock from a magma that is otherwise of mafic composition.

Group: IGNEOUS

Origin: Intrusive

Grain size: Medium

Crystal shape: Euhedral

Classification: Ultramafic

Occurrence: Pluton

Color: Dark, Medium