Granite and basalt are excellent examples of coarsely grained igneous rocks. The coarseness of such igneous rocks is a result of magma becoming trapped beneath sediment and stone, which allows the liquid to cool at a slower rate.
Rocks that originate by this slow process are classified as phaneritic. These contrast with aphanitic igneous, which are made up of microscopic grains, and igneous rock that is cooled so quickly it takes on characteristics of glass. The conditions necessary to form phaneritic rock leave it buried beneath the Earth's crust. Over time, wind and water work to erode the mineral material containing this slow-cooled magma, until finally it is exposed to the surface.