Sphalerite is a mineral composed of essentially zinc sulfide and is the principal ore of zinc. It also contains variable amounts of iron. When sphalerite has a high iron content, its opaque black variety is referred to as marmatite. Sphalerite is otherwise called by the miners as pyrite, false galena, mock lead, zinc blende and black jack. The approximate composition of a pure blende of sphalerite is 67 percent zinc and 33 percent sulfur. Sphalerite has got its name from a Greek word meaning "unfaithful rock," and it was named by E.F.Glocker in 1847.
The sphalerite mineral has a cubic crystal system. The zinc and sulfur atoms are coordinated tetrahedrally in the crystal structure. The crystal structure closely resembles the structure of a diamond crystal. When the crystalline structure of sphalerite exhibits a hexagonal analog, it is called the wurtzite structure.
Sphalerite is usually brown, yellow or gray to gray black and may be dull or shiny. Its luster resembles that of a diamond. It has light brown or yellow streak and a hardness of 3.5 to 4, along with a specific gravity of 3.9 to 4.1. Certain specimens such as gray black crystals exhibit a lustrous rainbow-like play of color, known as the ruby sphalerite.
Industrial Uses of Sphalerite
Sphalerite, being a chief source of zinc, is mainly used for metallurgy. The zinc is used to coat metals to avoid corrosion and to make metal blends. The zinc extracted from sphalerite is also used in rust-proofing materials and dietary supplements. It is even used in making copper, silver and lead. Sphalerite is also used to make brass, pigments, batteries and medicine.
Sphalerite is also used in the manufacture of luminous dials, television screens, X-ray screens, nontoxic paints and fluorescent lights. It is considered highly valuable in the jewelry and gem business. Its high refractive index (2.37 to 2.42) is important in gemology. Gemologists polish sphalerite and turn it into a beautiful ornament.
Availability of Sphalerite
Sphalerite is abundantly available in various parts of the world and is located in all of the continents except Antarctica. However, the transparent varieties of sphalerite are found only in Spain and Mexico.