Sphalerite

This mineral can be recognized by its striking resinous luster and perfect cleavage. The red variety is called "ruby blende" or "ruby zinc," while the dark varieties are known as "black jack." It is the most important ore of zinc, which is used in galvanizing iron, making brass paint, wood preservative, and in dyes and medicine. The name comes from the Greek word meaning "treacherous," an allusion to the ease with which dark varieties were mistaken for galena, but yielded no lead.

Mineral Photos courtesy of R.Weller/Cochise College