1. adj. [Geology]

Pertaining to minerals or igneous rocks composed of minerals that are rich in iron and magnesium, dense, and typically dark in color. The term comes from the words magnesium and ferric. Common mafic minerals are olivine and pyroxene. Basalt is a mafic igneous rock. (Compare with felsic.)

See: felsic,  igneous,  midoceanic ridge,  mineral