The Collaborative International Dictionary of English v.0.48:

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]

WordNet (r) 3.0 (2006):

pyroxene
    n 1: any of a group of crystalline silicate mineral common in
         igneous and metamorphic rocks