Primary Rocks also known as Igneous rocks, are formed from the solidification of molten rock material. These rocks originate from the cooling and crystallization of magma or lava.
Igneous rocks indicated volcanic eruption is done. And it is crystalline in nature which depend on rate of cooling. If it cools fast, it will make small crystal size and vice versa.
Primary rocks are of two types :- 1) Intrusive Rocks 2) Extrusive Rocks
1) Intrusive igneous rocks form below the earth surface, cooling slowly, which allows for the growth of large mineral crystals, such as granite.
2) Extrusive igneous rocks form on the earth’s surface, cooling rapidly, resulting in small mineral crystals like basalt.

Characteristic of igneous rocks:
1. Rocks are relatively harder, rapid, less porous and permeable which is dependent on the density of joints.
2. Igneous rocks are useless for paleontologist because of absence of fossil records.
3. Igneous rocks are rich in metal because it is formed due to solidification of magma.
4. Igneous rocks forms acidic and basic kind of igneous rocks:-
A) Acidic Igneous rocks – Low Concentration of metal and high concentration of silica content. It is light in color and has low density such as Granite.
B) Basic Igneous rocks – High Concentration of metal and low concentration of silica content. It is dark in color and high in density. Example is Basalt.