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Metamorphic rocks are formed from the transformation of existing rock to new kinds of rock in a process known as metamorphism. The original rock (protolith) is subjected to temperatures over 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar) or more. This leads to profound physical or chemical changes. During the process of metamorphism, the rock stays mostly in a solid-state. However, the rock gradually recrystallizes to a new texture or mineral composition. The rock may be an igneous, sedimentary, or existing metamorphic rock.
Metamorphic rocks make up a large part of the Earth’s crust and form 12% of the Earth’s land surface. Metamorphic rocks are classified based on their protolith, their chemical and mineral makeup as well as their texture. Metamorphic rocks may be formed simply by being deeply buried beneath the Earth’s surface, where they are subject to high temperatures and the great pressure of the rock layers above.
Some examples of metamorphic rocks include gneiss, slate, schist, marble, and quartzite.
Formation of metamorphic rocks
Metamorphic rocks are formed when rocks (sedimentary, igneous, and metamorphic) are subjected to high heat, high pressure, hot mineral-rich fluids, or commonly, some combination of all these factors deep within the earth or where tectonic plates see each other.
Metamorphism is known as heating the rocks at favourable temperature, pressure, and chemistry conditions without melting the rocks. However, this transforms the rock into denser, more compact rocks. During metamorphism, new minerals, textures, and structures like folds and foliations are formed either by mineral components rearrangement or by reactions with fluids that enter the rocks.
Sediments are metamorphosed into slates, phyllite/schist, gneiss, granulite, and finally eclogite—a process that is exemplified by pelitic rocks at a favourable temperature, pressure as well as chemistry conditions. Metamorphic rocks can also be classified based on their facies: zeolite—(Prehnite–pumpellyite/greenschist/blueschist)—amphibolites—gneiss—granulite—eclogite. Metamorphic rocks can also be categorized depending on the state of temperature and pressure; hornfels, sanidine, and skarns can be created.
Interesting facts on Metamorphic rocks
- Metamorphic comes from the ancient Greek word named “meta”, whose meaning is changed and “morphe”, whose meaning is formed.
- Metamorphic rocks are brought to the Earth’s surface with the help of uplift and erosion.
- Metamorphic rocks are classified into two categories, namely foliated metamorphic rocks and non-foliated metamorphic rocks.
- Metamorphic rocks and igneous and sedimentary rocks are classified based on grain size, shape, orientation, and mineral composition.
- Most of the Earth’s crust is formed with metamorphic rock.
- Marble is a metamorphic rock formed from the sedimentary rock of limestone.
- Granulite is a metamorphic rock formed out of the igneous rock of basalt.
- The famous Taj Mahal in India is one big metamorphic rock. This is because it is made up entirely of marble.
Conclusion
Metamorphic rocks are formed from the existing rocks with the help of a process called Metamorphosis. Metamorphosis is known as the process of converting rocks in high heat high pressure without actually melting the rocks. Metamorphic rocks are subjected to high heat, high pressure, and temperature conditions. Metamorphic rocks are utilized for everyday purposes. Some examples of metamorphic rocks are marble, graphite, diamond, iron, etc. Metamorphic rocks are classified into two categories, namely, Foliated metamorphic rocks as well as non-foliated metamorphic rocks.
