Metamorphic rocks are formed when rock changes over a period of time due to a lot of physical changes like pressure, heat and different chemical activity. When sedimentary rocks or igneous rocks go through the physical process such as pressure exposure, heat changes, and tectonic plate movement at the plate edges. These rock changes occur when these rocks are exposed to an environment.
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Due to thermal metamorphism, the materials of rocks are chemically modified and recrystallised. The thermal metamorphism is classified into:
- Contact metamorphism
- Regional metamorphism
Contact metamorphism
When rocks come in contact with hot intruding magma and lava, the rock recrystallize under high temperatures.
Regional metamorphism
Recrystallization of rocks takes place because of deformation created by tectonic shearing together with high temperature or pressure or both.
Types of Metamorphic Rocks
Types of metamorphic rocks are:
Foliated Metamorphic Rocks
On these rocks, one can witness the arrangement of certain mineral grains appearing like parallel stripes. Foliation occurs when pressure forces compress minerals within a rock to align in an elongate or flat way. These rocks form a sheet-like structure which reflects pressure applied direction.
Examples of foliated metamorphic rocks are granite, gneiss, and biotite schist.
Non-Foliated Metamorphic Rocks
These types of rocks are formed of minerals that are not flat or elongated. Here, the grains will not be aligned when pressure is applied. Layered or banded appearances are not seen on non-foliated metamorphic rocks.
Examples of foliated metamorphic rocks are skarn, novaculite, marble, hornfels, and quartzite.
Learn more about igneous rocks here.
Characteristics of Metamorphic Rock
- Cataclastic metamorphism occurs along with the tectonic plate faults where the rocks get rubbed with each other which results in the grain size reduction.
- Transformation of these rocks are classified as one which could not form non foliated rock and is of low grade.
- Circulation of rock results in huge number of mineral water chemical reactions which results in different kinds of precious metals and stones.
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