A metamorphic rock is a type of rock which has been changed by extreme heat and pressure. Its name is from ‘morph’ (meaning form), and ‘meta’ (meaning change).
The original rock gets heated (at temperatures greater than 150 to 200 °C) and pressured (1500 bars). This causes profound physical and/or chemical change. The original rock may be sedimentary rock, igneous rock or another older metamorphic rock.
There is always more pressure and higher temperature under the Earth’s surface. In the root of a mountain chain or a volcano, these forces will be enough to change the shape of the strata and the minerals it is made of. Sedimentary rock which has been near such forces often looks as if a giant had twisted it and heated it over a fire. Examples of metamorphic rock:
- Marble is a metamorphic rock formed from limestone.
- Slate is a metamorphic mudstone or shale.
- Quartzite is a metamorphic sandstone.
