Metamorphic rocks
The metamorphic rocks are formed by the transformation of pre-existing rocks (igneous, sedimentary) to a new type of rock and then followed by the process called metamorphism. The pre-existing rock subjected to high temperature (greater than 150 to 200 °C), high pressure, causes physical and chemical changes in the earth’s crust. The example of metamorphic rocks is- Gneiss, marble, slate, schist, etc.
The Process of Metamorphism:
In this process, the rocks transformed into denser, more compact rocks referred to as metamorphic rock. By rearrangement of components or by reaction with fluids in rocks the new mineral is created. The pressure and temperature can change previously metamorphosed rocks into new types of rocks. The metamorphic rock formed by metamorphosis is squished, smeared out, and folded.
The metamorphic rocks may be classified as:
- Common Metamorphic Rocks: Includes phyllite, schist, gneiss, quartzite, and marble.
- Foliated Metamorphic Rocks: Granite and biotite schist, these are strongly banded or foliated metamorphic rock.
- Non- Foliated Metamorphic Rocks: These rocks do not consist of platy or sheet-like structure. Limestone is not in a flat or elongated shape.
Types and examples of Metamorphic rocks:
| Metamorphic Rocks | Example |
| Gneiss
It is a very common and widely distributed metamorphic rock. The gneiss is formed due to high temp. and pressure, the result of high-grade regional metamorphism. Ortho gneiss is gneiss derived from igneous rock. Para gneiss is gneiss are metamorphic rock derived from sedimentary rock. |
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| Marble
Marble is formed by the metamorphosis of Limestone. the metamorphic rock produced under the condition of thermal metamorphism. |
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| Phyllite
It is a cleaved Metamorphic rock having affinities with both slate and mica – schist. |
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| Quartzite
Quartzite is a metamorphic arenaceous rock. It is formed when Quartz rich sandstone or chert has been exposed to high temperature and pressure. In this condition, the quartz grains get fused and a hard, dense irregular rock formation takes place. |
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| Schist
Schist is a well foliated, a higher degree of metamorphism, it medium to coarse-grained metamorphic rock. |
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| Slate
the slate is a metamorphic rock produced by the low-grade metamorphism of shale. It is a very fine-grained metamorphic rock. Its characteristics are excellent foliation called slaty cleavage. |
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Characteristics of Metamorphic Rocks:
- The metamorphic rocks were once igneous or sedimentary rocks, these are changed or metamorphosed due to intense heat and pressure within the earth’s crust.
- They are crystalline and often possess foliated texture.
- After metamorphosis, some rocks become harder than their original form, as diamond from carbon, Quartzite from sandstone, marble from limestone.
- The metamorphic rocks don’t contain fossils because the fossils of original sedimentary rocks destroyed during metamorphosis.
- These rocks are found in a wide range.
- The imperfectly foliated are coarse-grained metamorphic rocks. ex. gneisses
- The fine-grained metamorphic rocks are perfectly foliated. eg. Schist from Shale.
- Most gneissic metamorphic rocks consisting bands of granular quartz and feldspar.
You can also read:
references: https://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3459.html
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