Metamorphism may be defined as the process of transformation of igneous or sedimentary rocks to metamorphic rocks ( changed rocks ) through the Earth’s movements ( producing heat and pressure). The metamorphism can be thermal when the intrusion of the hot mass of igneous rock raises the temperature of surrounding rocks. Similarly, these can be the contact metamorphism when flowing when action by magma affects rocks in the zone near the batholiths or dike.
Metamorphism produces changes in the minerals. Mostly the change reshapes the rock particles along parallel planes which are different from the bedding. It is called flow cleavage and its best example is slate. Moreover, through the act of metamorphism fine-grained sediments such as shale are turned into Slates and Schists, coarse-grained or crystalline rocks form Quartzite, Gneisses, and Granulites, and most of the rocks show foliation. The processes which operate together in the affected rock to bring about metamorphism are (i) granulation, (ii) plastic deformation, (iii) recrystallization, and (iv) metasomatism.