BRONZITE  , a member of the

pyroxene group of minerals, belonging with enstatite and hypersthene to the orthorhombic series of the group . Rather than a distinct species, it is really a ferriferous variety of enstatite, which owing to partial alteration has acquired a bronze-like sub-metallic lustre on the cleavage surfaces . Enstatite is magnesium metasilicate, MgSiO3, with the magnesia partly replaced by small amounts (up to about 5%) of ferrous oxide; in the bronzite variety, (Mg,Fe)SiO3, the ferrous oxide ranges from about 5 to 14%, and with still more IV . 2I 64,1 iron there is a passage to hypersthene . The ferriferous varieties are liable to a particular kind of alteration, known as " schillerization," which results in the separation of the iron as very fine films of oxide and hydroxides along the cleavage cracks of. the mineral . The cleavage surfaces therefore exhibit a metallic sheen or " schiller," which is even more pronounced in hypersthene than in bronzite . The colour of bronzite is green or brown; its specific gravity is about 3.2—3•.3, varying with the amount of iron present . Like enstatite, bronzite is a constituent of many basic igneous rocks, such as, norites, gabbros, and especially peridotites, and of the serpentines which have been derived from them . It also occurs in some crystalline schists . Bronzite is sometimes cut and polished, usually in convex forms, for small ornamental objects, but its use for this purpose is less extensive than that of hypersthene . It often has a more or less distinct fibrous structure, and when this is pronounced the sheen has a certain resemblance to that of cat's-eye . Masses sufficiently large for cutting are found in the norite of the Kupferbergin the Fichtelgebirge, and in the serpentine of Kraubat near Leoben in Styria .

In this connexion mention may be made of an altered

form of enstatite or bronzite known as bastite or schiller-spar . Here, in addition to schillerization, the original enstatite has been altered by hydration And the product has approximately the composition of serpentine . In colour bastite is brown or green with the same metallic sheen as bronzite . The typical locality is Baste in the Radauthal, Harz, where patches of pale greyish-green bastite are embedded in a darker-coloured serpentine . This rock when cut and polished makes an effective decorative stone, although little used for that purpose . (L . J .