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peridotite Petrogr.|ˈpɛrɪdətaɪt|
[As used in English ad. G. peridotit (H. Rosenbusch Mikrosk. Physiogr. (1877) II. 522; previously F. péridotite had been used for an olivine-basalt (Cordier & d'Orbigny Descr. des Roches (1868) ii. 118); f. G. peridot, F. péridot peridot: see -ite1.]
Any of the group of plutonic rocks containing little or no feldspar but substantial olivine, usu. with pyroxene, amphibole, or other mafic minerals.
1878J. D. Dana Man. Mineral. & Lithol. (ed. 3) 451 Doleryte... There are two series: A. Ordinary, B. Chrysolitic, and for the latter the name Peridotyte has been used. 1882A. Geikie Text-bk. Geol. 151 A series of crystalline rocks composed essentially of olivine, with usually one or two other magnesium silicates..has been classed by Rosenbusch under the general name of Peridotites. 1897― Anc. Volcanoes Gt. Brit. I. 31 Picrites or other varieties of Peridotites. 1931S. J. Shand Study of Rocks vii. 114 Kimberlite.., the matrix of all African diamonds.., is a highly serpentinised peridotite. 1950E. E. Wahlstrom Introd. Theoret. Igneous Petrol. xiii. 291 Dunite, a variety of peridotite, is almost 100 per cent olivine. 1963[see melanocratic adj. s.v. melano-]. 1972Mineral. Mag. XXXVIII. 437 The peridotite consists dominantly of coarse-grained (2 mm) olivine with minor interstitial clinopyroxene and amphibole of similar grain size.
Hence peridoˈtitic a., containing, consisting of, or resembling peridotite.
1886J. J. H. Teall Brit. Petrogr. iv. 68 Peridotitic, hornblendic, and augitic rocks have been serpentinised. 1935Branson & Tarr Introd. Geol. iii. 13 Magmas occurring to depths of 10 miles are of one type, those that are 10 to 40 miles (the maximum thickness of the crust) down are of another type, and those in the layer (approximately 900 miles thick) next below the crust are of still another. These three regions of the earth's body are known as the granitic, gabbroid or basaltic, and peridotitic zones. 1971Nature 22 Oct. 522/2 The general hypothesis of sea-floor spreading envisages the upwelling of peridotitic mantle material beneath mid-oceanic ridges. 1974Mineral. Mag. XXXIX. 798 Peridotitic rocks in the Massif du Sud..have suffered about 30% serpentinization. |