BLENDE

BLENDE, in Mineralogy, the sulphuret of zinc, and by much the most common ore of that metal. In its crystalline form, its colour and appearance, this mineral varies extremely. The most common varieties, certainly, are brown or black, but a fine, oil-green, transparent species occurs at Schemnitz in Hungary; another of a rich hyacinth red colour is met with at Klapruck in Transylvania; and a third in botrioidal concretions, having a white fibrous structure, is found near Fowey in Cornwall. The fibrous blende of Prizham in Bohemia possesses, after a fresh fracture, a lustre almost metallic, and is peculiar, from the portion of cadmium with which it is associated. The crystalline form of blende is tessellar, and often presents the faces of the dodecahedron, to which figure the larger cleavable varieties are easily reducible by mechanical

division. The surfaces of the crystals are extremely re-splendent, and have at times a strong adamantine lustre. They yield to the knife, are rather brittle, and possess a specific gravity equal to 4.07. Blende, according to Thomson and Berthier, is composed of

When strongly heated in the oxidating flame of the blow-pipe, it gives off vapours of zinc, which form a coating on the charcoal; but it does not melt. It is soluble in nitric acid, during which process sulphuretted hydrogen is disengaged. Some varieties are phosphorescent in the dark when rubbed, and present that phenomenon even although the experiment be repeated under water. The sulphuret of zinc occurs both in primitive and secondary rocks, and is an almost constant accompaniment in the veins of lead, iron, and copper, associated with quartz, calcareous spar, or barytes. Great quantities of blende are found in Derbyshire and Cornwall, at Alston Moor and Lead Hills, at Klapruck in Transylvania, and Freyberg in Saxony; in Hungary, Bohemia, Silesia, and the Hartz. It is used in some places for obtaining the zinc in combination with it, but is otherwise an unimportant ore.