'Pyroxene' definitions:

Definition of 'pyroxene'

noun

Any of a group of crystalline silicate mineral common in igneous and metamorphic rocks

From: GCIDE

Pyroxene \Pyr"ox*ene\, n. [F. pyrox[`e]ne, from Gr. ? fire + ? a stranger; -- so called because it was supposed to the be a stranger, or of rare occurrence, in igneous rocks,] (Min.) A common mineral occurring in monoclinic crystals, with a prismatic angle of nearly 90[deg], and also in massive forms which are often laminated. It varies in color from white to dark green and black, and includes many varieties differing in color and composition, as diopside, malacolite, salite, coccolite, augite, etc. They are all silicates of lime and magnesia with sometimes alumina and iron. Pyroxene is an essential constituent of many rocks, especially basic igneous rocks, as basalt, gabbro, etc. [1913 Webster]
Note: The pyroxene group contains pyroxene proper, also the related orthorhombic species, enstatite, bronzite, hypersthene, and various monoclinic and triclinic species, as rhodonite, etc. [1913 Webster]