Here's a breakdown:
* Oceanic Crust: Primarily composed of basalt and gabbro, which are dense, mafic rocks rich in iron and magnesium.
* Continental Crust: Predominantly made up of granite and other felsic rocks, which are lighter and have higher concentrations of silica and aluminum.
Density:
* Mafic rocks (basalt and gabbro): Have higher density than felsic rocks (granite). This means they contain more mass packed into a smaller volume.
* Felsic rocks (granite): Have lower density due to their higher silica content.
Therefore, the denser composition of oceanic crust makes it heavier than continental crust. This difference in density is a crucial factor in plate tectonics, as it contributes to the subduction of oceanic crust beneath continental crust at convergent plate boundaries.