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HYPERSTHENE, a rock-forming mineral belonging to the group of orthorhombic pyroxenes. It differs from the other members (enstatite [q.v.] and bronzite) of this group in containing a considerable amount of iron replacing magnesium: the chemical formula is (Mg,Fe)SiOj. Distinctly developed crystals are rare, the mineral being usually found as foliated masses embedded in those igneous rocks norite, hypersthene-andesite, etc. of which it forms an essential constituent. The coarsely grained labradorite-hypersthene-rock (norite) of the island of St Paul off the coast of Labrador has furnished the most typical material; and for this reason the mineral has been known as " Labrador hornblende " or paulite. The colour is brownishblack, and the pleochrism strong; the hardness is 6, and the specific gravity 3-4-3-5. On certain surfaces it displays a brilliant copper-red metallic sheen or schiller, which has the same origin as the bronzy sheen of bronzite (q.v.) , but is even more pronounced. Like bronzite, it is sometimes cut and polished for ornamental purposes. (L. J. S.)

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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