orthogneissn.
/ˈɔːθə(ʊ)nʌɪs/, U.S. /ˈɔrθoʊˌnaɪs/ Geology.
A form of gneiss derived by metamorphism from igneous rocks. Cf. paragneiss n.
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the world > the earth > structure of the earth > constituent materials > rock > metamorphic rock > [noun] > gneiss > varieties of
ferberite1811
hälleflinta1878
orthogneiss1902
paragneiss1902
1902 A. Harker Petrol. (ed. 3) xxii. 331 All these have the chemical composition of sedimentary rocks; Rosenbusch styles them ‘paragneisses’, in contra-distinction to ‘orthogneisses’, which have the composition of, and are believed to represent, igneous rocks.
1932 A. Harker Metamorphism xvii. 271 The more or less distinctly banded crystalline rocks which are conveniently styled orthogneisses (in contradistinction to paragneisses, which are highly metamorphosed sediments) attain in some countries a vast development.
1962 Mineral. Abstr. 15 553/2 Alkaline syenitic orthogneisses form a lenticular body 5 km in length in biotite gneisses in the Cevadais area, near Ouguela, Alto Alentejo, Portugal.
1989 Nature 20 July 223/1 A foliated orthogneiss consisting of tonalitic and amphibolitic layers alternating on a centimetre scale.
This entry has been updated (OED Third Edition, September 2004; most recently modified version published online March 2022).
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n.1902