Question: What does the Bowen Reaction Series show about the mineral composition of igneous rocks? What does the Bowen Reaction Series show about the mineral composition of igneous rocks? Pyroxene and orthoclase are commonly found together. Calcium rich plagioclase is the first mineral to melt as a rock is heated. Peridotite in the mantle is usually molten. Aphanitic rocks are always mafic in composition. The minerals in igneous rocks form in separate groups that depend on the temperature at which they crystallize.