NET, IAS, State-SET (KSET, WBSET, MPSET, etc.), GATE, CUET, Olympiads etc.: Identification of Metamorphic Rocks
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Foliation | Grain Size | Hardness | Usual Color | Other | Rock Type |
foliated | fine | soft | dark | “tink” when struck | Slate |
foliated | fine | soft | dark | shiny; crinkly foliation | Phyllite |
foliated | coarse | hard | mixed dark and light | wrinkled foliation; often has large crystals | Schist |
foliated | coarse | hard | mixed | banded | Gneiss |
foliated | coarse | hard | mixed | distorted “melted” layers | Migmatite |
foliated | coarse | hard | dark | mostly hornblende | Amphibolite |
nonfoliated | fine | soft | greenish | shiny, mottled surface | Serpentinite |
nonfoliated | fine or coarse | hard | dark | dull and opaque colors, found near intrusions | Hornfels |
nonfoliated | coarse | hard | red and green | dense; garnet and pyroxene | Eclogite |
nonfoliated | coarse | soft | light | calcite or dolomite by the test | Marble |
nonfoliated | coarse | hard | light | quartz (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.