ECLOGITE (from Gr. EKXoyi, a selection)  , in petrology, a typical member of a small group of metamorphic rocks of special interest on account of the variety of minerals they contain and their microscopic structures and geological relationships . Typically they consist of pale green or nearly colourless augite (omphacite), green hornblende and pink garnet . Quartz also is usually present in these rocks,. but felspar is rare . The augite is mostly a variety of diopside and is only occasionally idiomorphic . The garnet sometimes forms good dodecahedra, but may occur as rounded grains, and encloses quartz, rutile, kyanite, and other minerals very frequently . The hornblende is usually pale green and feebly dichroic, but, in some eclogites which are allied to garnet-amphibolites, it is of dark brown colour . Among the commoner accessory minerals are kyanite (of blue or greyish-blue tints), rutile, biotite, epidote and zoisite, sphene, iron oxides, and B.C . 2000; obi . =23° 55.5' A.D . 1700; obi . =23° 1500 „ =23 52.3 1750 =23 1000 „ =23 48.9 1800 „ =23, 500 „ =23 .45.4 185o „ =23 0 „ =23 41.7 1900 „ =23 A.D . 500 „ =23 38.0 1950 „ =23 1000 „ =23 34.1 2000 „ =23 1500 „ =23 30.3 2050 „ =23 2000 „ =23 26.4 2100 „ =23 2500 =23 22.5 pyrites .

The rutile is invariably in small brown prisms; the kyanite forms bladed crystals, with perfect cleavage; felspar, if present, belongs to basic varieties

rich in lime . Other minerals which have been found in eclogites are bronzite, olivine and glaucophane . The last mentioned is a bright blue variety of hornblende with striking pleochroism . The eclogites in their chemical composition show close affinities to gabbros; they often exhibit relationships in the field which 'show that they were primarily intrusive rocks of igneous origin, and occasionally con-tact alteration can be traced in the adjacent schists . Examples are known in Saxony, Bavaria, Carinthia, Austria, Norway . A few eclogites also occur in the north-west highlands of Scotland . Glaucophane-eclogites have been met with in Italy and the Pennine Alps . Specimens of rock allied to eclogite have been found in the diamantiferous peridotite breccias of South Africa (the so-called " blue ground "), and this has given rise to the theory that these are the parent masses from which the Kimberley diamonds have come . (J . S .