1911 Encyclopædia Britannica/Stannite

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STANNITE, a rare mineral consisting of tin, copper and iron sulphide (a sulpho-stannate, Cu2FeSnS4), containing, when pure, tin 27.5, copper 29.5%. It has a metallic lustre, and, when pure, is iron-black in colour: more often, however, it is bronze-yellow, owing to tarnish or to the presence of intimately admixed chalcopyrite: for this reason it is known to miners as "bell-metal-ore" or as "tin pyrites." The hardness is 31/2 and the specific gravity 4.45. It usually occurs as granular to compact masses, rarely as crystals. Minute crystals from Bolivia have been shown to be tetragonal and hemihedral, like chalcopyrite; and to be invariably twinned, giving rise to pseudocubic forms. The mineral has been found in a number of Cornish tin mines, and was formerly worked to a limited extent as an ore. At Zinnwald in Bohemia it occurs with blende and galena, and in Bolivia with silver ores.  (L. J. S.)