Intrusive igneous rocks cool from magma slowly in the crust. They have large crystals. Extrusive igneous rocks cool from lava rapidly at the surface. The preexisting rocks may be igneous, sedimentary, or other metamorphic rocks. The word metamorphism is taken from the Greek for “change of form”; metamorphic rocks are derived from igneous or sedimentary rocks that have altered their form as a result of changes in their physical environment.