Peridotite

Peridotite is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron.

Peridotite is the dominant rock of the upper part of Earth’s mantle. The compositions nodules found in certain basalts are of special interest along with diamond pipes (kimberlite), because they provide samples of Earth’s mantle brought up from depths ranging from about 30 km to 200 km or more.

The word comes from the gemstone peridot, which consists of pale green olivine. Classic peridotite is bright green with some specks of black, although most hand samples tend to be darker green. While green and yellow are the most common colors, peridotitic rocks may exhibit a wide range of colors including blue, brown, and red.