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 (24 x 32 mm) under transient,cross-polarised light,explaining the lively colours 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 |