Physical Changes:
* Heat: Heat from deep within the Earth or from nearby igneous intrusions causes the minerals in sedimentary rocks to recrystallize. This can change the texture of the rock, making it more compact and dense.
* Pressure: The immense weight of overlying rock layers or tectonic forces can cause sedimentary rocks to deform and recrystallize. This pressure can also cause minerals to align in a specific direction, resulting in a layered or banded appearance.
Chemical Changes:
* Recrystallization: Minerals in sedimentary rocks can be chemically altered by heat and pressure, forming new minerals. This can change the composition and appearance of the rock.
* Dehydration: Water contained within sedimentary rocks is often driven out during metamorphism, further altering mineral composition.
* Reactions with Fluids: Hot, chemically-charged fluids circulating through sedimentary rocks can cause chemical reactions that lead to the formation of new minerals and the alteration of existing ones.
The Result: Metamorphic Rocks
Metamorphic rocks are classified based on their texture and mineral composition, which are influenced by the intensity of heat and pressure they experienced. Some common metamorphic rocks formed from sedimentary rocks include:
* Slate: Formed from shale by low-grade metamorphism.
* Marble: Formed from limestone by high-grade metamorphism.
* Quartzite: Formed from sandstone by high-grade metamorphism.
* Gneiss: Formed from a variety of sedimentary rocks by high-grade metamorphism.
Key Points:
* Metamorphism is a gradual process that occurs over long periods.
* The type of metamorphic rock formed depends on the original sedimentary rock and the degree of heat and pressure it experiences.
* Metamorphic rocks are important geological indicators of past geological events and provide insights into the Earth's internal processes.
