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The crust is composed of two basic rock types granite and basalt. The continental crust is composed mostly of granite. The oceanic crust consists of a volcanic lava rock called basalt.Basaltic rocks of the ocean plates are much denser and heavier than the granitic rock of the continental plates.arth's rocky surface is divided into two types: oceanic crust, with a thin dense crust about 10 km thick, and continental crust, with a thick light crust about 40 km thick.
The continental crust is the layer of granitic, sedimentary and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. It is less dense than the material of the Earth's mantle and thus floats on top of it. Continental crust is also less dense than oceanic crust, though it is considerably thicker; mostly 35 to 40 km versus the average oceanic thickness of around 7-10 km. About 40% of the Earth's surface is now underlain by continental crust.