Question

Which of the following types of rocks are formed by the lithification process?
1. Igneous rocks
2. Metamorphic rocks
3. Sedimentary rocks
4. Primary rocks

Answer 1

Correct Answer - Option 3 : Sedimentary rocks

The correct answer is Sedimentary rocks.

• Sedimentary rocks are formed by the lithification process.

• Lithification:
  • It refers to the process that loose and under-consolidated sediment particles transform into hard and solid rocks.
  • This process includes a number of geological processes, such as consolidation, deep bury, cementation, recrystallization and dehydration.
• Igneous Rocks
  • As igneous rocks form out of magma and lava from the interior of the earth, they are known as primary rocks.
  • The igneous rocks (Ignis – in Latin means ‘Fire’) are formed when magma cools and solidifies.
  • 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 earth’s crust or on the surface of the earth.
  • Igneous rocks are classified based on texture which depends upon the size and arrangement of grains or other physical conditions of the materials.
  • Granite, gabbro, pegmatite, basalt, volcanic breccia, and tuff are some of the examples of igneous rocks.
• Sedimentary Rocks
  • The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling.
  • Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents and are broken up into various sizes of fragments.
  • Such fragments are transported by different exogenous agencies and deposited.
  • These deposits through compaction turn into rocks.
  • In many sedimentary rocks, the layers of deposits retain their characteristics even after lithification.
  • Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale, geyserite, chalk, limestone, coal etc.
• Metamorphic Rocks
  • Metamorphic means ‘change of form’.
  • These rocks form under the action of pressure, volume, and temperature (PVT) change.
  • Metamorphism occurs 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 or the underlying rocks are subjected to great amounts of pressure by overlying rocks.
  • Metamorphic rocks are formed due to the proximity of sedimentary rocks with molten magma.
  • Mechanical disruption and reorganization of the original minerals within rocks due to breaking and crushing without any appreciable chemical changes are called dynamic metamorphism.
  • Examples- Marble, Quartzite, Schist, etc.