Question

How are igneous rocks classified and differentiated from each other?

Answer 1

Hint: A rock is a naturally occuring solid mass which is made of a mineral or a mixture of minerals. Rocks are further classified into three types- igneous rocks, metamorphic rocks and sedimentary rocks.

Complete answer: Igneous rocks are formed when lava or magma cools down near the surface of earth or inside it. Igneous rocks are also called primary rocks and form about 15% of earth’s crust. They are more commonly found in oceanic crust than continental crust.
-Igneous rocks are further classified into extrusive igneous rock and intrusive igneous rock.
-When magma cools down and solidifies within earth’s crust it's called intrusive igneous rock. As magma cools down slowly inside earth’s crust, intrusive rocks are coarse grained.Granite, gabbro and diorite are some examples of intrusive igneous rocks.
-When magma cools down on earth’s surface it is called extrusive igneous rock. Magma reaches earth’s surface due to volcanic eruptions and cools down rapidly. Rapid cooling of magma makes extrusive igneous rock fine grained. Basalt is a type of extrusive igneous rock and lava plateau and lava sheets are some common landforms formed by this kind of rock.
-Based on chemical composition, igneous rock is classified into felsic,intermediate, mafic and ultramafic rock. Felsic rocks are rich in feldspar and quartz, mafic rocks are rich in magnesium and iron, intermediate rocks have equal proportion of felsic and mafic minerals and ultramafic rocks are low in silica content and extremely high in mafic minerals.

Note: Batholiths , laccoliths, sill and dykes are some formations in which intrusive igneous rocks are found. One should also note that intrusive igneous rocks are also known as plutonic rocks and extrusive igneous rocks are called volcanic rocks.