Describe how igneous rocks are formed. State their main characteristics.

Igneous rocks are formed due to cooling, solidification and crystallisation of magma found at great depths in the interior of the earth.

The main characteristics of igneous rocks are-

1. They are hard and compact.
2. They are formed by solidification of molten magma.
3. They are granular and crystalline.
4. They are either fine grained, smooth and compact or may have large crystals with coarse texture.
5. The size of their crystals depends upon the rate of cooling of the molten material.
6. These rocks are less affected by chemical weathering because water does not percolate in these rocks.
7. Most of them consist of silicates.
8. They do not have layers. They are generally weathered by mechanical weathering.
9. They are associated with volcanic activity and are found mostly in volcanic regions.