What are the main rock types?

There are three major types of rocks. They are igneous rocks, sedimentary rocks and metamorphic rocks.

• Igneous rocks: When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks. 
• Sedimentary rocks: These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks.
• Metamorphic rocks: Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure.

Further Reading:

• The Rock Cycle
• Geography Notes