are formed by magma from the molten interior of the Earth. If magma erupts on the surface as lava, it will form extrusive rock, e.g. basalt. These rocks are formed when magma solidifies.

Pumice is an example of extrusive igneous rock. The word extrusive means that the magma was forced onto the earth's surface and cooled in a matter of hours. Granite is an example of intrusive ...