If Quartz is representative of the minerals in the rock granite, and olivine is representative of the minerals in the rock basalt, what can you infer about the density and iron content of the oceanic crust and continental crust?
The crust of Earth is split into two types: continental crust, oceanic crust. The total average composition of continental crust is similar to granite, which is a felsic rock. The composition of felsic rocks consists of quartz, mica and potassium rich feldspar. Feldpsar is the most abundant mineral in continental crust, the second place being occupied by silica, SiO_2. Feldspar represents a mixture of K, Ca, Na, Si and Al. There exists 7 types of feldspar, the limits between them being arbitrary.
The oceanic crust consists mostly of basalt, which is a mafic type of rock, it's content being rich in iron and magnesium. Basalt has the following mineral content: olivine, plagioclase feldspar, calcium, amphibole, and pyroxene.
Since mafic rocks consist of minerals having higher densities, the average density of basalt is 3 g/cm^3, while the average density of granite is 2.7 g/cm^3, the oceanic crust is much more denser than continental crust and much more thinner and younger.