Flexi Says: There are two kinds of crust. Oceanic crust is made of basalt lavas that flow onto the seafloor. Oceanic crust is relatively thin, between 5 to 12 km thick (3 to 8 miles). The rocks of the oceanic crust are denser (3.0 g/cm3) than the rocks that make up the continents. Thick layers of mud cover much of the ocean floor. Continental crust is much thicker than oceanic crust, with an average thickness of around 35 km (22 miles). The thickness of continental crust varies a lot from one location to another. Continental crust is made up of many different rocks. All three major rock types—igneous, metamorphic, and sedimentary—are found in the crust. On average, continental crust is much less dense (2.7 g/cm3) than oceanic crust. Since it is less dense, it rises higher above the mantle than oceanic crust.