It is often associated with blende and pyrites, and with calcite, fluorspar, quartz, barytes, chalybite and pearlspar as gangue minerals; in the upper oxidized parts of the deposits, cerussite and anglesite occur as alteration products.
A few varieties of blende are distinguished by special names, these varieties depending on differences in colour and chemical composition.
A pure white blende from Franklin in New Jersey is known as cleiophane; snow-white crystals are also found at Nordmark in Vermland, Sweden.
The Francke-Tina process, named from Francke, German consul at Bolivia, and tina, the wooden vat in which the process is carried out, was developed in Bolivia for the treatment of refractory ores rich in zinc blende and tetrahedrite (fahl-ore).
Such calciners are used especially in roasting zinc blende into zinc oxide, and in the conversion of copper sulphides into chlorides in the wet extraction process.
Crystals of blende are of very common occurrence, but owing to twinning and distortion and curvature of the faces, they are often rather complex and difficult to decipher.
Zinc sulphide, ZnS, occurs in nature as blende (q.v.), and is artificially obtained as a white precipitate by passing sulphuretted hydrogen into a neutral solution of a zinc salt.
Magnetic pyrites, copper pyrites, zinc blende and arsenical pyrites are other and less important examples, the last constituting the gold ore formerly worked in Silesia.
Twinning according to the first law is effected by rotation about an axis normal to the sphenoidal face (III), the resulting form resembling the twins of blende and spinel.
In roasting a ton of rich blende containing 60 per cent.