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Colour image of brown rock with black, white and gray spots
Peridotite. Belledune. Collector: unknown. New Brunswick Museum (NBMR 1811). Specimen width 14 cm. Peridotite is classified as an ultramafic rock, meaning it is dense and has less than 45% silica in its structure. It is mostly made of the minerals olivine and pyroxene. Peridotite is the rock type dominant in the upper part of the Earth’s mantle. It can be exposed at the surface during a process called obduction. Instead of the ocean crust being subducted back toward the mantle, a piece denser crust is pushed up and over the lighter crust. The group of rocks exposed at the surface is called an ophiolite and consists mostly of peridotite plus gabbro, pillow basalt and diabase sills and dikes.