The Metamorphic rock reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Metamorphic rock

Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, through which the protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another, older, metamorphic rock.

Metamorphic rocks make up a large part of the Earth's crust.

Metamorphic rocks are classified by texture and by chemical and mineral assembly (metamorphic facies).

Textures are separated into foliated and non-foliated categories. Foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage: for example, slate is a foliated metamorphic rock. Non-foliated rock does not have planar patterns of stress.

See also

• List of minerals
• List of rocks

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