The earth’s crust is divided into two crusts one being the continental crust and the other being the oceanic crust.The continental crust is 18.6-31 miles miles thick, and it is primarily composed of felsic rock.The primary rock found on the earth’s crust is the granite and igneous rock.Granite is an example of igneous rock once it cools.Then there is oceanic crust which is 4.3 miles thick and is primarily composed of mafic rock. Mafic rock contains magnesium and iron.There is basalt and gabbro rocks, basalt is a volcanic rock it comes through volcanoes.Even though the oceanic crust is thinner it is more dense.No machine has ever been able to drill a hole through the earth crust.One Russian group drilled at the Kola Super deep Borehole and the made it 40,230 ft below the surface which is the deepest hole there has ever been.