Nagaland PSC Exam: Identification of Metamorphic Rocks

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FoliationGrain SizeHardnessUsual ColorOtherRock Type
foliatedfinesoftdark“tink” when struckSlate
foliatedfinesoftdarkshiny; crinkly foliationPhyllite
foliatedcoarsehardmixed dark and lightwrinkled foliation; often has large crystalsSchist
foliatedcoarsehardmixeddistorted “melted” layersMigmatite
foliatedcoarseharddarkmostly hornblendeAmphibolite
nonfoliatedfinesoftgreenishshiny, mottled surfaceSerpentinite
nonfoliatedfine or coarseharddarkdull and opaque colors, found near intrusionsHornfels
nonfoliatedcoarsehardred and greendense; garnet and pyroxeneEclogite
nonfoliatedcoarsesoftlightcalcite or dolomite by the testMarble
nonfoliatedcoarsehardlightquartz (no fizzing with acid)Quartzite

Metamorphic rocks are the third great class of rocks. These are what happens when sedimentary and igneous rocks become changed, or metamorphosed, by conditions underground. The four main agents that metamorphose rocks are heat, pressure, fluids and strain. These agents can act and interact in an infinite variety of ways. As a result, most of the thousands of rare minerals known to science occur in metamorphic ( “shape-changed” ) rocks. Metamorphism acts at two scales, the regional scale and the local scale.

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