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BRONZITE

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Originally appearing in Volume V04, Page 641 of the 1911 Encyclopedia Britannica.
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BRONZITE , a member of the See also:

pyroxene See also:group of minerals, belonging with See also:enstatite and See also:hypersthene to the orthorhombic See also:series of the group. Rather than a distinct See also:species, it is really a ferriferous variety of enstatite, which owing to partial alteration has acquired a See also:bronze-like sub-metallic lustre on the cleavage surfaces. Enstatite is See also:magnesium metasilicate, MgSiO3, with the See also:magnesia partly replaced by small amounts (up to about 5%) of ferrous See also: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 See also:iron there is a passage to hypersthene. The ferriferous varieties are liable to a particular See also:kind of alteration, known as " schillerization," which results in the separation of the iron as very See also:fine films of oxide and hydroxides along the cleavage cracks of. the See also:mineral. The cleavage surfaces therefore exhibit a metallic sheen or " See also:schiller," which is even more pronounced in hypersthene than in bronzite. The See also:colour of bronzite is See also:green or See also:brown; its specific gravity is about 3.2—3•.3, varying with the amount of iron See also: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 See also:schists. Bronzite is sometimes cut and polished, usually in See also:convex forms, for small ornamental See also: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 See also:cat's-See also:eye. Masses sufficiently large for cutting are found in the norite of the Kupferbergin the See also:Fichtelgebirge, and in the See also:serpentine of Kraubat near See also:Leoben in See also:Styria.

In this connexion mention may be made of an altered See also:

form of enstatite or bronzite known as bastite or schiller-spar. Here, in addition to schillerization, the See also:original enstatite has been altered by hydration And the product has approximately the See also: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 See also:pale greyish-green bastite are embedded in a darker-coloured serpentine. This See also:rock when cut and polished makes an effective decorative See also:stone, although little used for that purpose. (L. J.

End of Article: BRONZITE

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