views updated May 08 2018

hypersthene A member of the orthorhombic pyroxenes with approximately equal amounts of Fe and Mg in its composition MgFeSi2O6, it is a mineral occurring within the series enstatite to (ortho) ferrosilite, although the name hypersthene has fallen into disuse (with the more general term orthopyroxene followed by the exact composition being preferred); sp. gr. 3.5; hardness 5–6; orthorhombic; green to greenish, or brownish-black; vitreous lustre; crystals can be prismatic or tabular, but usually irregular grains; cleavage good, prismatic {110}; occuss in iron-rich, bafic, igneous rocks, e.g. noritic gabbro, trachytes, and andesites.