Describe the characteristics and types of primary rocks. UPSC MAINS 2022 - General Studies Paper 1
A primary rock is a rock whose constituents are newly formed and have never been constituents of some other rock or formed through replacement and alterations. These are basically crystalline rocks with no organic remains on them. Igneous rock is a Primary Rock, as these are formed when hot magma cools down and solidifies. Igneous rocks are further classified into intrusive igneous rocks and extrusive igneous rocks. Intrusive or plutonic igneous rocks are formed when magma is trapped inside earth and cools down slowly over years forming coarse grained rocks.
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Intrusive Igneous Rocks
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Extrusive Igneous Rocks
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1.The igneous rocks found below the surface of the Earth are known as intrusive igneous rocks.
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The igneous rocks found on the surface of the Earth are known as extrusive igneous rocks.
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2.These are formed when the magma cools and solidifies below the Earth''s surface.
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These are formed when the lava cools and solidifies after reaching the Earth''s surface during a volcanic eruption.
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3. Examples: Granite and dolerite
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Examples: Basalt and obsidian
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Characteristics of Primary Rocks
- They are unfossiliferous : Any fossils are burnt away due to high temperature.
- Texture of the rocks: The grains are either coarse or fine which is reflective of the rate of cooling of magma.
- Mineral Rich: Since their origin is directly from the magma, they are rich in minerals especially ferrous minerals.
- Colour of the rocks: Colour of the rocks reflects its composition. Dark colour usually indicates basic magma as its source and light colour indicates acidic magma.
Primary rocks are an important source of information about the geology of an area, as they provide insight into the composition and temperature of the magma or lava that formed them. They are also an important resource for various industries, including construction and manufacturing.
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