Eclogite

eclogite

Any member of metamorphic rocks whose original composition is similar to that of basalt. Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other minerals such as kyanite and rutile. These minerals in the eclogite are the result of reactions in originally igneous minerals having been subjected to extremely high pressures and moderate to relatively high temperatures.

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eclogite [′ek·lə‚jīt]

(petrology)

A class of metamorphic rocks distinguished by their composition, consisting essentially of omphacite and pyrope with small amounts of diopside, enstatite, olivine, kyanite, rutile, and rarely, diamond.

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Eclogite 

a metamorphic rock, composed chiefly of clinopy-roxene and garnet. The clinopyroxene (omphacite) is a mixture of diopside, hedenbergite, and jadeite components; the mixed-composition garnet contains pyrope and almandine, as well as variable amounts of grossularite and andradite. Eclogite varieties with significant amounts of grossularite and disthene (kyanite) are called grospydites.

Various types of eclogite are distinguished according to the content of secondary minerals, including amphibole, enstatite, olivine, plagioclase, kyanite (disthene), corundum, rutile, graphite, and diamond-containing eclogites. Three types are distinguished on the basis of geological conditions of occurrence: the eclogites of the metamorphic zone, which are associated with glaucophane schists and alpine-type hyperbasites; the eclogites of granulite, gneiss, and amphibolite metamorphic complexes; and eclogites that form inclusions (xenoliths) in kimberlites and alkali basaltoids. The first two are formed within the crust; the last is of mantle origin. Deposits of rutile are associated with eclogite, and diamonds are found among the most deep-seated eclogites in kimberlite pipes.

A. A. MARAKUSHEV