Question

describe the nature and mode of origin of the chief types of rock at the earth crust?
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Answer 1

Answer:

Explanation:

Three types of Rocks: Igneous, Sedimentary, and Metamorphic.

Mode of origin:

Igneous Rocks: solidified from magma and lava,

Sedimentary Rocks: the result of deposition of fragments of rocks by exogenous process

Metamorphic Rocks – formed out of existing rocks undergoing recrystallisation

Different Nature of these rocks:

1. Igneous Rocks:

They are rough hard rocks and water percolates with great difficulty along the joints. The igneous rocks are granular or crystalline rocks. They do not have strata like sedimentary rocks. The igneous rocks are less affected by chemical weathering Igneous rocks do not contain fossils. They mostly associated with volcanic activities.

2. Sedimentary rocks:

Sedimentary rocks are formed of sediments derived from the older rocks, plant and animal remains and thus rocks contain fossils of plants and animals.

They are found over the largest surface area of the globe.

Sedimentary rocks contain several layers but these are seldom crystalline rocks. Layers of sedimentary rocks are seldom found in original and horizontal manner.

They may well consolidate, poorly consolidated and even unconsolidated. They are characterized by different types of joints. These are generally perpendicular to the bedding planes.

3. Metamorphic rocks:

Foliation, streaking or parallel arrangement of the constituent crystals is the most common characteristic feature of metamorphic rocks. They split along the bedding planes known as fissility. The structure of the presence of numerous closely spaced parallel planes of splitting is known as cleavage.

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