Granite is a felsic igneous rock rich in quartz and feldspar with low iron-magnesium mineral content, whereas basalt is a mafic igneous rock rich in iron- and magnesium-bearing minerals (pyroxene, olivine) and magnetite. Density and magnetic susceptibility of igneous rocks both broadly increase with mafic (Fe-Mg-rich) mineral content.
Because granite has a much lower proportion of iron- and magnesium-bearing (mafic) minerals compared to basalt, it is lighter (lower density, roughly 2.7 g/cc vs...
Full option-by-option analysis available to enrolled students.