Gems Notes and Extracts Augusto Castellani, Mrs. John Brogden 1871

. 1178 GEMS.LXXIX.PYROXENUM.THIS name is given to certain substances found byHaiiy, scattered in lava and in rocks of igneous origin,to which he thought them quite foreign, whence thename of 7r9p, fire,and eyos, stranger.For a long time they were confounded with the amphibole,with which they have in common the form of thecrystal and its components, but in different proportions.That which distinguishes the pyroxenum from theamphibole completely is its inferior brightness, its vitreouslight, and, above all, its cleavage in three differentplanes parallel to the base.The colours of the pyroxenum are black, dark green,white, and grey.Its most common crystals are differentprisms with oblique axes ; they are, however, sometimesmet with in irregular octahedral prisms, more or lessmodified, and in pebbles either granular or of a densesubstance.All these crystals are generally small ;their specificgravity is from 3-1 to 3-4, and their very variable conformationyields on analysisSilex 48 to 52Chalk .. .. 13 to 24Alumina .. .. 3 to 5Magnesia.. .. 8 to 10Oxide of iron . . 1 2 to 14Oxide of manganese.to 2