QUE : Briefly classify rocks based on their formation.

 Rock is the upper crust of the earth’s surface made of solid, igneous materials. The upper crust of the earth is also called the crust or rock. Rocks are formed by the combination of different substances. These substances are called minerals. Thus, an organized mass of one or more mineral substances is called a rock.

•  Based on the formation process, there are 3 primary types of rocks:

• Igneous rock
• Sedimentary rock
• Metamorphic rock.
  
• Types of rocks
  

• Igneous rocks: Since the earth’s crust is hot, the rocks formed by the solidification of its red substance – magma in various forms are known as igneous rocks.
  
•  Since these rocks were formed first, they are also called ‘primary rocks’.
  
•  Igneous rocks can be divided into internal and external igneous rocks. In which internal igneous rocks are formed by cooling of magma at depth and various types of rocks are formed from it when magma solidifies.
  
•  Granite is a good example of internal igneous rock. These rocks are found in the plateaus of South India, Rajasthan and Madhya Pradesh.
  
•  Often magma is solidified between the basement and external rocks that do not come to the surface, due to which forms like sills, dikes, litholites and laccoliths are formed and often during volcanic activity, magma breaks through the layers and comes out and when the lava comes into contact with the outside air, it cools rapidly, crystals are found in it in very fine form. E.g. basalt.
  
•  Sedimentary rocks: Due to weathering and erosion forces, igneous rocks break down and are deposited in water, forming layers. Chemical and organic substances are often found in them.

•  According to these substances, sedimentary rocks can be divided into 3 types: Sedimentary rocks made of rock material – such as clay, conglomerate rock. Sedimentary rocks made of chemical material – such as shale and salt rock. Sedimentary rocks made of organic material – such as limestone and coal.
  
•  Metamorphic rocks: The newly formed rocks formed by changing the original structure and form of igneous and sedimentary rocks are called metamorphic rocks. These rocks change due to physical and chemical changes and form new crystals.
  
•  Often, the structure and form of rocks change over a very wide area as a result of temperature and pressure. Ex – Quartzite and Marble.
  
•  Various rocks like mineral coal, basalt, marble can not only strengthen the geographical position but also the economic condition of the country.