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Describe the nature and mode of origin of the chief types of rock at the earth’s crust

Question:

Describe the nature and mode of origin of the chief types of rock at the earth’s crust. How will you distinguish them?

Answer:

Earth's crust is the top layer of earth in solid form. It is made up of three types of rocks.

  • Igneous rocks
  • Sedimentary rocks
  • Metamorphic rocks

Igneous rocks:

Mode of origin of Igneous rocks:

It is primary rock and made up of the cooling of molten magma. 

Nature of Igneous rocks:

  • It is very hard and not get weathered easily.
  • Igneous rocks are granular and they do not have layered like sedimentary rocks.
  • They do not contain any fossil remains.
  • For example, Granite, gabbro, basalt, etc.

Sedimentary rocks.

Sedimentary rocks are secondary rocks.

Mode of origin of sedimentary rocks:

Sedimentary rocks are formed by the lithification process of sediments.

Nature of sediments rocks:

  • It is not as hard as Igneous rocks.
  • It gets weathered easily.
  • It has a layered structure and contains fossils of plants and animals.
  • For example, sandstone, limestone, coal, potash, etc.

Metamorphic rocks:

Metamorphic rocks are also secondary rocks as it is derived from Igneous rocks and sedimentary rocks.

Metamorphic means "change of form".

Mode of origin of metamorphic rocks:

Under the action of PVT( pressure, volume, and temperature) and changes of PVT, a new form of rocks emerged which has different property than igneous and sedimentary rocks are called metamorphic rocks.

Nature of metamorphic rocks:

  • Due to PVT, the rock gets recrystallized and minerals or grains get arranged in layered or lines; such arrangement is called foliation or lineation.
  • Foliation or alienation, and banding are important features of metamorphic rocks.
  • For example, granite, slate, marble, etc.
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