Eclogite

Eclogite is a moderate to deep regional metamorphic rock composed mainly of omphacite and calcium-containing pyrope and almandine. Secondary minerals include quartz, spinel, olivine, enstatite, kyanite, rutile and zoisite. Ultra-high-pressure minerals such as coesite and diamond are sometimes present and can indicate the geologic environment in which the rock formed. Eclogite has no plagioclase, a high density (generally 3.6–3.9 g/cm³), a medium to coarse uneven granoblastic texture, a flaky structure, and a chemical composition similar to basalt. The composition of eclogite is complex and diverse. It can be in the form of lenses in the amphibolite facies metamorphic rock or in the glaucophane-lawsonite facies metamorphic rock. It can also exist in the form of xenoliths in layered ultramafic rocks or kimberlites. Eclogites form at high or ultra-high pressures (generally between 1–3 pascals) and high temperatures (generally between 450 and 750 °C). The cause of eclogite formation is...