Eclogite

A metamorphic rock made up of garnet, usually of the almandine-pyrope type, set in a matrix of the sodium rich pyroxene omphacite, representing one of the highest pressure metamorphic facies found in the Earth's crust and mantle. Eclogite typically forms from the high to ultrahigh pressure metamorphism of mafic rock along low thermal gradients of less than 10 degrees Celsius per kilometer, as oceanic crust is subducted down to the lower crust or upper mantle in a subduction zone, conditions that correspond to pressures at or above 12 kilobars and moderately high to very high temperatures. Beyond its defining garnet and omphacite, eclogite can contain accessory minerals such as kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum and, rarely, diamond, and geologists classify eclogites into three groups based on their dominant mineral chemistry. Its origin is debated, with evidence supporting derivation from both subducted oceanic crust and mantle material depending on the specific occurrence, and the partial melting of eclogite is thought to produce important igneous rocks and to contribute to volcanic regions that erupt unusually large volumes of magma.