Igneous rock was the first rock on our planet. The word igneous has been derived from Latin phrase which means ‘made from fire’. When magma cools and changes its form to solid, igneous rocks are formed. This process can occur below or above the earth’s surface.
Types of igneous rocks: –
The type of formed igneous rock can be determined by the exact location of the formation process. There are two types of igneous rocks: –
- Intrusive: – Formation of these rocks takes place within earth’s crust, under the surface. They are also known as ‘Plutonic Rocks’.
Example: – Granite
- Extrusive: – Formation of extrusive rocks takes place above the surface of earth. They are also known as ‘Volcanic Rocks’.
Example: – Obsidian
Quick Facts: –
- About 95% part of earth’s crust is made up of igneous rock. Even earth’s moon is made up of igneous rock.
- The lightest rock on the earth, Pumice rock is also an igneous rock.
- Igneous rocks are helpful in the growth of plants because they contain many minerals which can help a plant to grow.
- Intrusive igneous rocks have a grainy structure because their formation process is slow.
- Extrusive igneous rocks have a glassy structure because of their rapid formation.
- The Ocean floor is made out of hard and black basalt rock which is an extrusive igneous rock.
- A very large intrusive igneous rock which is extended in a mountain up to an unknown depth in earth’s crust is called batholiths.
- These batholiths can be as large as 97 km across.
- There are about 700 known types of igneous rocks.