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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