What is metamorphic rock with example? How metamorphic rocks are formed?

Metamorphic rocks are formed from older rocks. The older rocks may be either sedimentary or igneous rocks. When old rocks are experienced high temperature, pressure, and shearing stress at a considerable depth in the earth's crust, then the older rocks change chemically, structurally, and mineralogically by producing rocks with new texture and chemical composition, such rocks are called metamorphic rocks. The process in which the older rocks start to melt due to high pressure and temperature and are recrystallized with new minerals composition, such process is called metamorphism.

The agents, which are responsible for bringing about metamorphic changes or the agents of metamorphism are as follows-

1) Temperature: Temperature is one of the most important agents or factors of metamorphism. Due to high temperatures, pre-existing rocks like igneous and sedimentary started to melt by changing their texture and chemical composition and slowly converted into metamorphic rocks.

2) Pressure: Pressure plays an important role in the process of metamorphism. It is also an important factor of metamorphism. Due to pressure, mainly the structure of rocks is changed. In metamorphism, there are two types of pressure are mainly involved-

a) Hydrostatic pressure: Hydrostatic pressure is also known as load pressure because this pressure is developed due to overlying loads. This pressure has another name called uniform pressure. This pressure increases with an increase in depth. It is able to change the volume and density of the parent rocks.

b) Directed pressure: Directed pressure is also known as differential pressure. This pressure is mainly responsible for the change in shape, the orientation of minerals, development of fracture, and formation of minor folds, etc. It is produced mostly by orogenic movement ( When two objects move toward each other ). It dominates at or near the surface. It results in the crushing and granulation of minerals, without the formation of any new mineral.

3) Chemically active fluid: Most commonly, the fluid is water-containing ions in solution in which, many minerals are hydrated (have water bound chemically) and thus contain water within their crystalline structures. It is also an important metamorphism agent or factor. It percolates through the intergranular space of rocks and brings metamorphism. Water is the main chemically active fluid. Water act as a solvent for catalyst, which helps in a different chemical reaction, and as a result, some new minerals are formed. The source of these chemical agents is generally the intrusive igneous body within the country rocks.

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