Igneous Rock


The word ‘igneous’ is derived from the Latin word ‘Ignis’ which means ‘fire’. Igneous rock is formed due to cooling, solidification, and crystallization of magma and Lava that come out from the interior of the earth. Thus, it is known as primary rocks. The process of cooling and solidification of molten rock can happen within the earth’s crust or on the surface of the earth’s crust. therefore, on the basis of occurrence, it can be classified into two major groups i.e., Intrusive Igneous rock and Extrusive Igneous Rock.

INTRUSIVE IGNEOUS ROCKS- when the magma does not reach the earth’s surface and solidify within the earth’s crust then these kinds of igneous rocks are known as Intrusive Igneous rocks. Examples; laccoliths, lopoliths, batholiths, sills, dykes, and granite.

EXTRUSIVE IGNEOUS ROCKS- The igneous rock formed due to the cooling and solidification of lava at the surface of the earth is known as Extrusive Igneous Rock. Examples, basalt, gabbro, and obsidian.

It can be classified into three sizes i.e., small, medium, and large.

LARGE IGNEOUS ROCK- when molten rock cools down and solidifies within the earth’s crust then very large size of mineral grains is formed. For example- Laccolith and dykes etc.

MEDIUM IGNEOUS ROCK- Intermediate cooling conditions at the surface would result in intermediate sizes of mineral grains.

SMALL IGNEOUS ROCK- when cooling suddenly occurs, then very small and fine mineral grains solidify and form igneous rock at the surface of the earth.

Examples of Igneous rocks are granite, gabbro, basalt, tuff, etc.