How many rock types are there?

There are many different kinds of rocks that are grouped under three families on the basis of their mode of formation. They are: 

• Igneous Rocks: solidified from magma and lava; 
• Sedimentary Rocks: the result of deposition of fragments of rocks by exogenous processes; 
• Metamorphic Rocks: formed out of existing rocks undergoing recrystallisation.

Further Reading:

• The Rock Cycle
• Geography Notes