1. Recrystallization:
* The heat causes the minerals within the sedimentary rock to become unstable and rearrange their atoms.
* This process leads to the formation of new minerals with a different crystal structure, often larger and more tightly packed.
2. Texture Changes:
* The pressure causes the rock to become more compact and dense.
* The original sedimentary structures (like layering) can be deformed or even erased, resulting in a new, often foliated texture (like slate or schist).
3. Mineral Changes:
* The combination of heat and pressure can cause the original minerals to react and form new ones.
* This can lead to the creation of minerals that are not found in sedimentary rocks, like garnet or staurolite.
The type of metamorphic rock that forms depends on the intensity of heat and pressure, as well as the original composition of the sedimentary rock.
Here are some examples:
* Low-grade metamorphism: Results in rocks like slate, which are relatively fine-grained and have a distinct foliation.
* High-grade metamorphism: Can produce rocks like gneiss, which have a banded appearance due to the segregation of minerals.
* Contact metamorphism: Occurs when a sedimentary rock comes into contact with an igneous intrusion (like a magma chamber). This leads to localized heat and pressure, often creating rocks like marble.
In essence, heat and pressure transform a sedimentary rock's physical and chemical properties, resulting in a completely different rock type – a metamorphic rock.
