Pyroxene in felsic matrix
pyroxene (py'-rox-ene, py-rox'-ene) (a) A group of dark rock-forming silicate minerals, closely related in crystal form and composition and having the general formula: Si4012, where A Ca, Na, Mg, or Fe2+, and B Mg, Fe2+, Fe3+ Cr, Mn, or Al, with silicon sometimes replaced in part by aluminum. It is characterized by a single chain of tetrahedra with a silicon:oxygen ratio of 1:3; by short,
stout prismatic crystals; and by good prismatic cleavage in two directions parallel to the crystal faces and intersecting at angles of about 870 and 930. Colors range from white to dark green or black. Pyroxenes may crystallize in the orthorhombic or monoclinic systems; they constitute a common
constituent of igneous rocks, and are similar in chemical composition to the amphiboles (except that the pyroxenes lack hydroxyls). (b) A mineral of the pyroxene group, such as enstatite, hypersthene, diopside, hedenbergite, acmite, jadeite, pigeonite, and esp. augite. Etymol: Greek "pyros", "fire", +
"xenos", "stranger" , apparently so named from the mistaken belief that the pyroxenes "were only accidentally caught up in the lavas that contain them" (Challinor, 1978, p.250). Pron: pie-rok-seen or peer-ok-seen." Glossary of Geology Fifth Edition
