How are intrusive and extrusive classified?
Intrusive or extrusive describe properties of an igneous rock. An intrusive rock is formed within the crust and it insulated and cooled slowly. Some examples of an intrusive rock include diorite, granite, gabbro, and periodite. They have large grains because they have more time for growth. On the other hand, extrusive rocks cool at the surface rapidly. They are comprised of tiny crystals and/or glass. Some examples include rhyolite, andesite, and basalt.