The process of metamorphism of the Metamorphic Rocks are classified mainly into four parts:
1. Thermal Metamorphism: When the rocks are exposed to magma at the time of volcanic activity, then the metamorphism takes place due to high heat in the rocks near the volcanic tube, this is called Thermal Metamorphism. Sometimes water gets mixed with the magma, due to which chemical changes also occur in rocks. This type of metamorphism takes place in limited area. Thus, its geographical importance, is very low.
2. Dynamic or Regional Metamorphism: This type of metamorphism takes place in a vast area. Compression and heat both have the effect in it. This type of metamorphism occurs often in folded mountainous areas. This type of metamorphosed rocks become crystallized. If the original rock is already crystallized, then new formation of crystals begins in it in a new way.
3. Hydro Metamorphism: In this type of metamorphism, change in the minerals of rock takes place in the form of a solution by mixing of chemical substances with water. Depth of excessive water also increases the weight and pressure. Due to this process, metamorphism in the rocks takes place.
4. Thermo – Hydro Metamorphism: When there is hot water over the rocks, then due to pressure and water vapour, this type of metamorphism takes place in the rocks. Such type of metamorphism is not geographically important.
These forms of metamorphism are shown with the help of the following fig.