The earth’s crust Is composed of various kinds of rocks. Everything which forms the crust of the earth is called the rocks. There are three main kinds of rocks, each formed In a different way.

Igneous rocks:

Igneous rocks are those which have been formed by the cooling of the magma. Basalt and granite are the most Important examples of the igneous rocks.

Sedimentry rocks:


Rocks formed by the deposition of layers of sediments are called sedimentry rocks. Limestone, sandstone, clay, coal are the examples of the sedimentry rocks.

Metamorphic rocks:

Rocks which have been formed by changing their original forms due to excessive heat and great pressure. Marble slate, quartzite and gneiss are the examples of the metamorphic rocks.

Important questions


1. What Is Magma ?

Ans. Very deep below the surface of the earth, rocks are found In the molten state due to the high temperature. This molten state of reek Is called magma,

2. What are ores ?

Ans. Seme rocks contain useful minerals from which metals are extracted. These minerals are called ores.


3. Of which type of the rocks most of the earth’s crust are made up ?

Ans. Igneous rocks.

4. What Is the Important characteristic of sedimentry rock ?

Ans. It Is made up of layer


5. In which of the rocks does petroleum occur?

Ans. Sedimentry rocks.