- a silicate mineral, chiefly of calcium, magnesium, iron, and aluminum: a dark-green to black variety of monoclinic pyroxene, characteristic of basic rocks.
- a black or greenish-black mineral of the pyroxene group, found in igneous rocks. Composition: calcium magnesium iron aluminium silicate. General formula: (Ca,Mg,Fe,Al)(Si,Al) 2 O 6 . Crystal structure: monoclinic
