<Tr> <Td> Shield Platform Orogen Basin Large igneous province Extended crust </Td> <Td> Oceanic crust: 0--20 Ma 20--65 Ma> 65 Ma </Td> </Tr> <P> Igneous rock (derived from the Latin word ignis meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic . Igneous rock is formed through the cooling and solidification of magma or lava . The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust . Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition . Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks . Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses . </P> <P> Igneous and metamorphic rocks make up 90--95% of the top 16 km of the Earth's crust by volume . Igneous rocks form about 15% of the Earth's current land surface . Most of the Earth's oceanic crust is made of igneous rock . </P> <P> Igneous rocks are also geologically important because: </P>

What rock is found 10 kilometers beneath the earth's surface