A term qualifying the composition of igneous rocks, minerals, or magmas. Mafic rocks are dark-colored reflecting their high content of iron and magnesium-rich minerals (biotite, amphibole, pyroxene, olivine, and calcium-rich plagioclase feldspar). Consequentially, these rocks contain fewer silica-rich (felsic) minerals (quartz, potassium feldspar, muscovite, and sodium-rich plagioclase feldspar).