Sometimes, magma cool down within the ground under the earth's surface. Intrusive igneous rocks are formed when magma cools under the ground while extrusive igneous rocks are formed when magma cools on the surface.
If Intrusive rocks cool down slowly; they have large grains and coarse texture. Examples of Intrusive igneous rocks are granite , basalt , batholiths , laccoliths , dikes , and sills
If extrusive rocks cool down very fast; they have very small or no grains and smooth texture. Examples of extrusive igneous rocks are basalt , rhyolite , pumice , and obsidian.