Hypersthene

Hypersthene, one of the rhombic pyroxene group of minerals. It is a silicate of magnesium and iron, containing from 11 to 26 per cent. of the former, and from 10 to 34 per cent. of the latter.

It crystallises in the Prismatic system, in forms identical with those of enstatite, and has a well-developed cleavage, so as to be very generally foliated. It is brownish green, greyish, or nearly black, with a pearly or coppery metalloid lustre on the cleavage surfaces. It is brittle; but has a hardness of 5 to 6, and specific gravity of 33 to 3-4. It may be translucent, and is distinctly pleochroic. It fuses to a black enamel or to a magnetic mass. With labradorite felspar it forms the rock hypersthenite, and it is a frequent accessory mineral, especially in schists. It occurs largely in the Cuillin Hills of Skye.