Question

Classify and explain the rocks.

Answer 1

• Igneous:
  The igneous rocks are formed by the solidification of molten magma. Also called Primary or Parent Rocks. Types:

1. Extrusive Igneous Rocks:
   Molten magma which comes out from the interior of the earth’s surface gets solidified and forms such rocks. Fine-grained and glassy in nature. Eg., Basalt, found in north western peninsular India.
2. Intrusive Igneous rocks:
   Molten magma cools down deep inside the earth’s crust, becomes solid, and forms such rocks. Form large grains. Deep-seated rocks are plutonic rock and ones at shallow depths – Hypabysal rocks. Example Granite, Diorite.

• Sedimentary:
  Formed by the sediments derived and deposited by various agents. Also called stratified rocks. Types:

1. Organic sedimentary rocks:
   Formed due to decomposition of dead Plants and Animals. Contains fossils. Example Chalk, Talc
2.  Mechanical sedimentary rocks:
   Formed from the disintegration of Igneous and metamorphic rocks. Get deposited due to erosion by natural agents. Get cemented after a long time to form rocks. Example Sandstone, Shale.
3. Chemical sedimentary rocks:
   Formed by precipitating of minerals from water. Formed due to evaporation of the chemical-rich solution. Example Rock Salt.

• Metamorphic:
  Formed when Igneous and sedimentary rocks are subjected to high temperature and pressure. Types:
  

1. Thermal Metamorphic:
   If the change in rocks is caused by high temperature.
2. Dynamic Metamorphic:
   If the change in rock is caused by high pressure. Formed from Igneous rocks. Eg., Granite into gneiss
   Formed from Sedimentary rocks. Eg., Shale into Slate