Metamorphism     Any type of rock—igneous, sedimentary, or metamorphic—can become a metamorphic rock. All that is needed is enough heat and/or pressure to alter the parent rock’s physical or chemical makeup without melting the rock entirely.     Rocks change during metamorphism because their minerals must be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange so new minerals form. Ions may move between minerals to create minerals with different chemical compositions.     Extreme pressure exerted from one... Show more

Metamorphism    
Any type of rock—igneous, sedimentary, or metamorphic—can become a metamorphic rock. All that is needed is enough heat and/or pressure to alter the parent rock’s physical or chemical makeup without melting the rock entirely.    
Rocks change during metamorphism because their minerals must be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange so new minerals form. Ions may move between minerals to create minerals with different chemical compositions.    
Extreme pressure exerted from one direction only may cause foliation. During this process, layers form in rocks as they are squeezed by extreme pressure. Examples of foliated metamorphic rocks include slate and schist, both of which form from the sedimentary rock shale. Metamorphic rocks may also be non-foliated. Quartzite and marble are nonfoliated metamorphic rocks.    

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