Sphalerite (ZnS) is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but often contains some iron as (Zn,Fe)S. It is usually found in association with galena, pyrite, and other sulfides along with calcite, dolomite, and fluorite. Miners have also been known to refer to sphalerite as zinc blende, mock lead, false galena and black-jack.
Its color is usually yellow, brown, or gray to gray-black, and it may be shiny or dull. Its luster is resinous. It has a yellow or light brown streak, a hardness of 2.5 - 4, and a specific gravity of 3.9-4.1. Some specimens have a red iridescence within the gray-black crystals; these are called "ruby sphalerite." The pale yellow and red varieties have very little iron and are translucent. The darker more opaque varieties contain more iron. Some specimens are also fluorescent in ultraviolet light. Sphalerite crystallizes in the isometric crystal system.
These distortions of the hexagonal lattice, which are likely to be related to the phase transition in ZnO, are discussed with special reference to the theory of Keffer and Portis in term of the partial polar binding in wurtzite type compounds.
The zincblende structure is face centered cubic and can be considered as composed of cubic close packed tetrahedra.
The phase transitions of wurtzite or zincblende structure to rocksalt one are rapid and reversible, so that the quenching method often used for the determination of phase stability in oxides can't be used.
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