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Rock Cycle Notes for UPSC - Types of Rocks & Explanation with Diagram
IMPORTANT LINKS
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GS Paper |
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Topics for UPSC Prelims |
Weathering of Rocks, Geological Survey of India (GSI) |
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Topics for UPSC Mains |
What is the Rock Cycle?
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Key Facts on the Rock Cycle for UPSC |
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Feature |
Details |
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Definition |
Continuous process of rocks changing from one type to another over geological time. |
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Igneous, Sedimentary, Metamorphic |
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Igneous Formation |
Cooling and solidification of magma (intrusive) or lava (extrusive). |
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Sedimentary Formation |
Weathering, erosion, transport, deposition, and lithification of sediments. |
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Metamorphic Formation |
Transformation of existing rocks due to heat, pressure, or chemical reactions. |
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Key Processes |
Melting |
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Cooling & Solidification |
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Weathering & Erosion |
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Deposition |
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Lithification |
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Metamorphism |
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Driving Forces |
Plate tectonics (mountain building, volcanism) |
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Weathering & Erosion |
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Heat from Earth's interior |
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Time Scale |
Occurs over millions to billions of years (geological time). |
The rock cycle is an ever-running process through which rocks are formed, destroyed, and reconstructed in time. The process comprises three main kinds of rocks: igneous, sedimentary, and metamorphic. Igneous rocks result from cooled molten material, sedimentary rocks result from pressed sediments, and metamorphic rocks result when rocks already present are subjected to heat and pressure. The cycle illustrates how these rocks are able to change into each other by processes such as weathering, erosion, melting, and pressure. This cycle is significant in the shaping of the Earth's surface.
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Types of Rocks
There are three main types of rocks:
Igneous Rocks
These form from the cooling and solidification of molten rock (magma or lava). Igneous rocks examples include granite, basalt, and pumice.
Sedimentary Rocks
These are formed from the accumulation and compression of sediments (such as sand, mud, or organic material). Over time, they harden into rock. Sedimentary rocks examples include sandstone, limestone, and shale.
Metamorphic Rocks
These are the rocks that come into being after pre-existing rocks (either sedimentary, igneous, or other metamorphic rocks) experience heat and pressure at high intensity, which modifies them structurally and compositionally. Metamorphic rocks examples include marble (from limestone) and slate (from shale).
You might like to read: Earth – Origin and Evolution NCERT notes!
Steps Involved in Rock Cycle
There are a number of steps through which rock is undergoing transformation from one type to another type, i.e., the process of the rock cycle. The main processes that take place during the rock cycle are crystallization, erosion and sedimentation, and metamorphism.
Crystallization
Cooling of magma either underground or on the surface leads to the formation of igneous rocks. With cooling of magma, formation of different crystals occurs at different temperatures. For example: at higher temperature the mineral olivine crystallizes out of magma. Formation of olive minerals requires more temperature than quartz. The cooling rate of magma determines how much time the crystals will take to form. Slower the cooling rate larger will be the crystals.
Erosion and Sedimentation
The weathering process wears the rocks present at the surface of Earth into smaller pieces. These smaller fragments are called sediments. Sources like running water, ice, gravity help in transporting all these sediments from one place to another place. During this process, the sediments are laid down or deposited. These deposits further lead to the formation of sedimentary rock, the accumulated sediment must become compacted and cemented together.
You might also like: NCERT notes on Structure of the Earth!
Metamorphism
Further when rock gets exposed with extreme heat and pressure within the Earth but after that also they do not melt, then the rock becomes metamorphosed. By this process the composition of minerals can be changed along with the texture of rocks. Because of that reason, a metamorphic rock may have a new mineral composition and/or texture.
Also read: NCERT notes on Physical Weathering!
Forces Driving the Rock Cycle
Forces that dictate the rock cycle are enumerated below:
- Plate tectonics: Lithospheric plate movement and interaction are primarily responsible for contributing to the rock cycle. They create mountains, cause earthquakes and volcanic eruptions.
- Spreading ridges: Spreading ridges are where the tectonic plates are separating. This causes molten material from the mantle to rise and create a new oceanic crust.
- Subduction zones: Subduction zones are where a tectonic plate is pushed under another. This produces melting of the plate that is going down and volcanic arcs.
- Continental collision: Two colliding continental plates may lead to the uplift of massive mountain ranges such as the Himalayas and the formation of metamorphic rocks.
- Accelerated erosion: Erosion mechanisms, including weathering, transportation, and deposition, are constantly disintegrating rocks into sediments. These can be compacted and cemented to create sedimentary rocks.
- Water: Water acts as a powerful force in the rock cycle. It contributes to weathering, erosion, transportation, and deposition of sediments. It also plays a role in the formation of sedimentary rocks through processes like compaction and cementation.
You might also like to read Environment NCERT notes!
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Rock Cycle UPSC FAQs
What do you mean by a rock cycle?
The rock cycle is the continuous process through which rocks transform from one type to another over time due to geological processes such as heat, pressure, and weathering.
What are the 5 processes of the rock cycle?
The five processes are: melting, cooling, weathering, compaction, and cementation.
What are the different types of rocks?
The three main types of rocks are igneous, sedimentary, and metamorphic.
How are metamorphic rocks formed?
Metamorphic rocks are formed when existing rocks are subjected to intense heat and pressure, causing them to change in structure and composition.
How are extrusive and intrusive rocks formed?
Extrusive rocks are formed when magma cools quickly on the Earth’s surface, while intrusive rocks are formed when magma cools slowly beneath the surface.