Minerals or rocks that are rich in iron (Fe) and magnesium (Mg), such as olivine and pyroxene.

It describes the rock-forming silicate minerals that contain essential iron (Fe) and/or magnesium (Mg). The very common ferromagnesian minerals include olivine, pyroxene, amphibole and mica.

minerals containing iron and magnesium (usually dark-colored) such as biotite, hornblende, augite, and olivine.