Question

Explain the formation of different types of rocks. Give examples of each.

Answer 1

On the basis of their formation, rocks are classified into the following three categories:

1. Igneous rocks: Lava is the hot molten magma that reaches the Earth's surface through cracks and crevices during a volcanic eruption. This cools down and solidifies below the Earth's surface or on it to form rocks. These rocks are known as igneous rocks.
Examples: Granite and basalt

2. Sedimentary rocks: The igneous rocks are broken down into smaller fragments by running water, waves, winds and moving ice. These fragments of rocks, known as sediments, are carried by rivers and are deposited at the floor of the lakes, oceans and seas. These fragments get compressed and cemented together due to extreme pressure, thereby, forming rocks. These rocks are formed in layers and are known as sedimentary or stratified rocks.
Examples: Sandstone and gypsum

3. Metamorphic rocks: Igneous and sedimentary rocks undergo a change in their characteristics and forms when they are subjected to extreme heat and pressure, volcanic activities or movements in the Earth's surface. The change leads to the formation of rocks known as metamorphic rocks.
Examples: Quartzite and marble