Peridotite is a non-specific name used for coarse-grained, dark-colored, igneous rocks. Formed in the upper part of the mantle, just below the Earth's crust, peridotite is known as a plutonic rock, or alternatively ultramafic, indicating that the rock contains less than 45% silica. It is here seen in a thin section (20 x 32 mm) in transient, cross-polarized light, explaining the lively colors of olivine, which is the primary mineral in peridotite, together with other mafic minerals such as pyroxenes and amphiboles. The content of quartz and feldspar is small. |