These are bodies of igneous rock, often ore-bearing, that have risen as liquid magma from Earth's interior but solidified before they reached the surface.
Australian geologists summoned the hunt for precious minerals in Antartic say they have for the first time discovered the deposits of the igneous rock that yields diamonds.Here's Matt McGrath.
The third type of rock are the metamorphics, and the metamorphics can either be sedimentary or igneous rocks that have been changed by heat and pressure deep underground.