The nature of the igneous and sedimentary rocks changes due to the effects of tremendous heat or pressure, and newly transformed rocks, called metamorphic rocks, are formed.
Quartzite is a hard, non-foliated metamorphic rock that was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts.
Minerals in the rocks get restructured on account of heat and pressure. This brings about a change in the original formation of rocks.
When existing rocks are subjected to high temperature and pressure, metamorphic rocks are formed. Metamorphism is a process by which these metamorphic rocks are formed. It is of three kinds:
Types of Metamorphism
Thermal metamorphism: Metamorphism caused by extreme temperature is called thermal metamorphism. It occurs because of the heat generated by magma or due to the friction caused by two moving rocks. Example: Forming of slate from clay
Dynamic metamorphism: It occurs when changes in rocks take place because of large-scale movements of the Earth’s crust. The rock may get pushed to greater depths under the surface of the Earth resulting in the formation of new rocks. Example: Shale gets converted to hornfels.
Regional metamorphism: When metamorphism is caused by large-scale changes such as mountain building, the igneous and sedimentary rocks may get buried to form new rocks. This is known as regional metamorphism. When only a small area is affected, it is called local or contact metamorphism. Example: Sandstone changes into quartzite.
Processes of Metamorphism
Mechanical metamorphism: It occurs when the texture of rocks is changed by crushing and rubbing processes. In this process, shales develop into slaty splits.
Chemical recombination: This process takes place when rocks containing more than one mineral are metamorphosed into one rock.
Chemical replacement: When liquids and gases enter the surface of the Earth through small cracks, they undergo chemical changes and new rocks are formed.
Recrystallization: It takes place when minerals present in rocks are changed into large crystals before metamorphism.
Also, Read Igneous Rocks