Primary rocks are also known as igneous rocks. They are called primary because igneous rocks originated first from all the rocks. They were formed during formation of upper crust of earth on cooling, solidification and crystallization of hot magma and lava.

The characteristics of primary rocks are:

• These rocks are hard rock and water percolates with great difficulty. The rocks become soft sometimes due to exposure to environmental conditions for long duration. Example: Basalt.
• These rocks are  granular or crystalline rocks but varies in size, form and texture of grains as these properties depend upon cooling, solidification of magma.
• Primary rocks or igneous rocks do not have strata like sedimentary rocks rather it has layers of lavas. Example: Valleys of Krishna river, Saraswati river etc.
• These rocks do not contain fossils as primary rocks were formed during origin of earth, there was no life on newly born earth.
• These rocks are associated with volcanic activities and are also known as volcanic rocks.

Types of primary rocks on basis of mode of occurrence:

• Intrusive igneous rocks:
  • Putonic igneous rocks- Granite
  •  Hypabyssal igneous rocks- Batholith, Laccolith etc.
• Extrusive igneous rocks: explosive type, quiet type.