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Formation Of Rocks

Rocks are aggregates of minerals. A mineral is an inorganic, crystalline solid. This means that it has a regular, repeating series of molecules...

Rocks are aggregates of minerals. A mineral is an inorganic, crystalline solid. This means that it has a regular, repeating series of molecules that ultimately determine its form. Quartz is an example of a very common mineral. Another is halite, commonly known as table salt. You can have very large quantities of a particular mineral, and even very large single crystals of minerals. Once you have more than one mineral together though, you’ve got a rock.

Igneous Rocks

  • It is formed out of magma and lava from the interior of the earth.
  • They are also known as primary rocks.
  • When magma in its upward movement cools and turns into a solid form it is called igneous rock.
  • The process of cooling and solidification can happen in the crust of the earth or on the surface of the earth.
  • Igneous rocks are classified based on texture.
  • If the molten material is
    • Cooled slowly at great depths, mineral grains may be very large.
    • Sudden cooling at the surface results in small and smooth grains.
    • Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks.
  • Examples of igneous rocks
    • Granite
    • Gabbro
    • Pegmatite
    • Basalt
    • Volcanic
    • Breccia
    • Tuff

Sedimentary Rocks

  • In Latin, the word ‘sedimentum’ means settling, derived from sedimentary
  • Due to prolonged exposure to denudational agents, rocks are broken into various fragments
  • Exogenous agents transport these rocks fragments. And get deposited in some places. By compaction, deposits turn to form rocks. This process is called lithification
  • The thickness of sedimentary rocks varies by the number of layers like sandstone, shale, etc
Based on the mode of formation, it is classified into three types.
1) Mechanically formed – 
  1. Sandstone.
  2. Conglomerate.
  3. Limestone.
  4. Shale, and loess, etc.
2) Organically formed-
  1. Geyserite.
  2. Chalk.
  3. Limestone, coal, etc.
3) Chemically formed –
  1. Chert.
  2. Limestone.
  3. Halite.
  4. Potash.

Metamorphic Rocks

  • Rocks which are formed under the action of volume, pressure, and temperature (PVT) changes are called metamorphic rocks.
  • The process when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks is called a metamorphic process.
  • Because of the process of thermal metamorphism, the materials of rocks get chemically modified and recrystallized.
  • Types of metamorphism:
    • Thermal metamorphism: Metamorphism occurs because of the influence of heat, it is called Thermal Metamorphism. They are of three types:
      • Contact metamorphism: When rocks come in contact with hot intruding magma and lava and the rock materials recrystallize under high temperatures, then such metamorphism is called contact metamorphism.
      • Regional metamorphism: When rocks undergo recrystallization due to deformation caused by tectonic shearing together with high temperature or pressure or both then it is called regional metamorphism.
      • Dynamic metamorphism: Metamorphism occurs without any appreciable chemical change, then it is called dynamic metamorphism. For example: granite is converted into gneiss; clay and shale are transformed into schist.
  • Examples of metamorphic rocks are:
  1. Gneissoid.
  2. Granite.
  3. Syenite.
  4. Slate.
  5. Schist.
  6. Marble.
  7. Quartzite.

Formation Of Rocks,Formation Of Rocks

Read Also: Energy Resources

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