The term ‘olivine’ is also used for a group of related minerals that all share similar crystal structures and the same general chemical composition of X 2 SiO 4, where X can stand for iron (Fe), magnesium (Mg), calcium (Ca), manganese (Mn) or nickel (Ni).uartz can only form from magmas that are relative rich in silica, while the olivine minerals only form from magmas that are relatively lean in silica, so quartz and olivine are incompatible minerals.