1. Mineral Recrystallization:
* Heat: Provides the energy for atoms within the existing minerals to break their bonds and rearrange into new, more stable mineral structures. This can change the size, shape, and arrangement of the crystals.
* Pressure: Can cause minerals to align themselves in a preferred direction, creating a foliated texture. This is often seen in rocks like schist and gneiss.
2. Chemical Changes:
* Recrystallization can involve the formation of new minerals from the existing ones. This often happens when elements are added or removed from the rock due to fluids circulating through the rock.
* Fluid Interactions: The presence of fluids like water can significantly influence the process of metamorphism. Fluids can transport elements, promote chemical reactions, and even dissolve existing minerals.
3. Texture Changes:
* Foliation: As mentioned earlier, pressure can create a layered or banded texture. This occurs when platy minerals like mica align themselves parallel to the direction of pressure.
* Non-foliated: Rocks that experience high heat but less directional pressure may develop a non-foliated texture, like marble.
4. From One Metamorphic Rock to Another:
* Progressive Metamorphism: The more intense the heat and pressure, the more the original rock is transformed. This leads to a sequence of metamorphic rocks, starting from low-grade rocks like slate, progressing to high-grade rocks like gneiss.
It's important to remember that metamorphism is a continuous process:
* There is no clear-cut point where a rock becomes metamorphic. It's a spectrum, and the degree of transformation depends on the intensity and duration of the heat and pressure.
* Existing metamorphic rocks can undergo further metamorphism, even transforming into entirely different types of metamorphic rocks.
In essence, each time a metamorphic rock is exposed to extreme heat and pressure, it is further transformed, leading to a new rock with different mineral composition, texture, and properties.
