BRONZITE

This article appears in Volume V04, Page 641 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: BRI-BUN

BRONZITE , a member of the pyroxene group of minerals, belonging with

enstatite

ENSTATITE

and hypersthene to the orthorhombic

series

SERIES (a Latin word from serere, to join)

of the group. Rather than a distinct species, it is really a ferriferous variety of

enstatite

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

MAGNESIA

partly replaced by small amounts (up to about 5%) of ferrous

oxide

OXIDE

; in the bronzite variety, (Mg,Fe)SiO3, the ferrous

oxide

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

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 3.23.3, 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

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

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

PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; "
pole
" is from the same original source)

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. S.)

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