Sphalerite also called zincblende or blackjack


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Sphalerite specimen also called zincblende or blackjack

Mineral Group  sulphide
Composition  ZnS
dimension (cm)  9x4x3
weight (g)  92
Sphalerite derives its name from the Greek sphaleros (`deceitful’, `uncertain’). This is because it occurs in such varied colours that even expert miners often failed to recognise it. Even in the 16th century they still mistook it for silver ore; only in the first half of the 18th century was it discovered that sphalerite contains a significant amount of zinc. ft was, however, not used for practical purposes till the 1860s, when a metallurgical method for extracting zinc from it was worked out. Until then it had been thrown away as useless gangue, especially as it was considered an unwelcome impurity in lead ores which caused difficulties in their metallurgical processing. It is usually granular; on crevices it forms crystals of perfect cleavage and of strong metallic lustre. ft is one of the most common sulphides and occurs in ore veins, usually with galena and pyrite, and sometimes chalcopyrite (polymetallic ores). The largest sphalerite deposits are in the regions of the upper Mississippi in the USA, and in Europe on the border of Germany and Belgium. Other important deposits are at Bleiberg in Carinthia (Austria), Pribram (Czech Republic) and Bytom in Polish Silesia. Magnificent specimens of yellow crystals have been found in north-western Spain in the Picos de Europa. That particular sphalerite is ground as a precious stone. Sphalerite is the main ore of zinc, which is used mainly for metal sheets and coatings resistant to oxidation. Gallium, indium and germanium, having semiconductor properties, are present as impurities in sphalerite and are recovered from it.
Wurtzite has the same chemical composition but differs in its internal structure and therefore also in the shape of its crystals (which are hexagonal). Unlike sphalerite it is comparatively rare; usually it is brown to yellow-brown, kidney-shaped or cup-shaped, radially acicular. ft is found in association with sphalerite and galena in polymetallic ore veins.
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Additional information

Weight 92 g
Dimensions 9 x 4 x 3 cm