Orthogneiss | geology | Britannica (original) (raw)

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gneiss

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  In gneiss
  Orthogneiss is formed by the metamorphism of igneous rocks; paragneiss results from the metamorphism of sedimentary rocks. Pencil gneiss contains rod-shaped individual minerals or segregations of minerals, and augen gneiss contains stubby lenses of feldspar and quartz having the appearance of eyes scattered through the…
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granulite–gneiss belts

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  In Precambrian: Granulite-gneiss rock types
  Orthogneisses of deformed and recrystallized tonalite (a granitic-type rock rich in plagioclase feldspar) and granite constitute the most common rock type. The geochemical signature of these rocks closely resembles that of modern equivalents that occur in granitic batholiths in the Andes. Where such rocks have…
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