Here's a breakdown:

* Oceanic crust:

* Average thickness: 5-10 kilometers (3-6 miles)

* Primarily composed of basalt and gabbro (mafic rocks)

* Denser than continental crust

* Continental crust:

* Average thickness: 35-70 kilometers (22-43 miles)

* Composed of a variety of rocks, including granite, gneiss, and sedimentary rocks (felsic and intermediate rocks)

* Less dense than oceanic crust

This difference in thickness and density plays a crucial role in plate tectonics. For example, when oceanic and continental plates collide, the denser oceanic crust is subducted (forced under) the less dense continental crust.