Blende

Blende, the name of which mineral signifies blind or deceptive, is known to English miners as "black-jack,"and, though containing no lead,sometimes resembles galena, lead sulphide. Formerly considered worthless, blende, which is zinc sulphide (ZnS), is now the chief commercial ore of zinc. Iron and cadmium are often present in this ore, and the rare elements, lithium, indium, thallium and gallium, have been detected in it, especially in its darker varieties. Blende only fuses on thin edges alone, but decrepitates before the blowpipe. With carbonate of soda it gives a green flame, and when intensely heated it yields the white incrustation characteristic of zinc, that becomes green with cobalt nitrate. It dissolves in concentrated nitric acid, leaving the sulphur as a residue, and in hydrochloric acid with disengagement of sulphuretted hydrogen. This and its greater softness distinguishes it from tinstone, which it often resembles in its adamantine lustre and black and brown colour. Its hardness is between 3.5 and 4, and its specific gravity 3.9 to 4.2. It is very brittle. It may be colourless or white and transparent yellow, green, or red, but is more often opaque and dark. It crystallises in tetrahedra and other forms in the cubic system; but may be fibrous or compact. It is abundant in Cornwall, Alston Moor, and elsewhere, associated with galena; at Ammeberg on Lake Wetter, in gneiss; in Asturias, with liquid enclosures; in Missouri; and in Franklin co., New Jersey, where the finest colourless crystals are found.