Question

Why are igneous rocks called primary rocks?

Answer 1

Hint: Rocks are defined as naturally occurring aggregates of minerals or mineraloid matter which form the outer layer or crust of the Earth. The study of rocks is known as petrology.

Complete answer:
Rocks are mainly divided into three different types- sedimentary rocks, igneous rocks and metamorphic rocks based on how they are formed. Sedimentary rocks are formed from existing particles of rocks, organisms and minerals in water that ultimately sediments to form a solution which then undergoes compaction and cementation at specified pressure and temperatures leading to the formation of sedimentary rocks.

Igneous rocks are those which are mostly formed by the cooling and solidification of the magma or lava and are further subdivided into two types-plutonic rock and volcanic rock. Plutonic rocks are formed when the magma cools followed by crystallization on the surface of Earth and volcanic rocks form when the magma forms minerals. Metamorphic rocks are any type of rock that has undergone physical as well as chemical changes resulting in the formation of a new type of rock.

Igneous rocks are known as primary rocks because they were the first ones to be formed in the rock cycle and do not contain any organic remains. The other two types are called secondary rocks because they have been formed from previous rocks remains and also comprises of organic matter.

Note: Rocks are important for humans as they are required in different processes such as development of buildings for which rocks with high strength are required, mining where valuable minerals are obtained from the rocks and few rocks are also helpful in the laboratory for research purposes.