1. Heat: The rock must be exposed to high temperatures, typically exceeding 200°C (392°F). This can happen due to:
* Contact metamorphism: When magma or lava comes into contact with existing rock.
* Regional metamorphism: When large-scale tectonic forces cause rocks to be buried deep within the Earth's crust.
2. Pressure: The rock also needs to be subjected to high pressure. This pressure can be:
* Confining pressure: Pressure from all directions due to burial under other rocks.
* Differential pressure: Pressure that is greater in one direction than another, often caused by tectonic forces.
3. Chemical reactions: The heat and pressure cause chemical reactions to occur within the rock, leading to the formation of new minerals. This process is called recrystallization.
4. Changes in texture: The original texture of the rock can be altered. For example, crystals can grow larger, minerals can be arranged in bands, or the rock can become foliated (layered).
Key points to remember:
* Metamorphism doesn't melt the rock, it simply changes its composition and texture.
* The original rock type (igneous, sedimentary, or even another metamorphic rock) is important, as it determines what kind of metamorphic rock will be formed.
* Metamorphic rocks are often formed in deep underground environments but can be exposed at the surface due to erosion and uplift.
Examples of metamorphic rocks:
* Marble: Formed from limestone
* Slate: Formed from shale
* Gneiss: Formed from granite or other igneous rocks
* Schist: Formed from shale or other sedimentary rocks
