The Olivine normally crystalizes first from the magma of the mafic minerals, It crystalizes at between 1200°C and 1300°C. when the temperature of magma drops and there is a silica still remains in the magma so the olivine reacts with this silica to form pyroxene.and by more cooling of the temperature of magma and there is a silica still remains in magma pyroxene change to amphibole, and amphibole to biotite.when the pyroxene strat to form the plagioclase feldspar also forms.