Gabbro is a rock found along mid-ocean ridges and ancient mountains composed of raised oceanic crust. It is formed when magma cools within the Earth's crust.
Gabbro has the same geological composition as basalt. Unlike basalt, however, gabbro never makes it to the surface of the Earth before cooling. It is often found under basalt, very deep in the ocean crust. On land, gabbroic rocks form part of the Wichita Mountains in the southwest of the state of Oklahoma. They were formed when magmatic activity in the area was induced by continental rifting about 500 million years ago during the Cambrian Period.