Felsic rocks contain a lot of sodium, potassium and calcium (and a great deal of aluminum), while mafic rocks consist of a lot of magnesium with iron....
Why is this?
Why is magnesium (z=12) in the denser rock(s) with iron (z=26), while aluminum (13) and calcium (20) get stuck nearer the surface with lightweight sodium (11)?
I haven't found a reason for this...
P.S.: What about potassium and sodium? Are they also unable to easily fit into iron rocks as well? After all, they also end up, generally, closer to the surface....