Eclogites and the Eclogite Facies

Abstract

The rock name eclogite was coined by Haüy, a founder of crystallography, in 1822. Since the original definition of the name was vague, its meaning was gradually settled through its usage in later years. According to the generally established usage in the first half of the twentieth century, it means a rock mainly composed of omphacite and almandine-pyrope-grossular garnet. Omphacite is a clinopyroxene containing diopside, hedenbergite and jadeite components, and quite frequently some acmite. However, no rigid limitations were given for the composition ranges of these minerals. Thus, some authors called diopside-almandine rocks eclogite. Small amounts of quartz, kyanite, olivine, orthopyroxene, amphibole and rutile may be present, but not plagioclase.