Sphalerite is a somewhat common zinc sulfide mineral (ZnS). It has a metallic to submetallic to resinous to adamantine luster. Many metals can substitute for the zinc, such as iron, cadmium, and manganese. Sphalerite almost always has some iron in it, so a better chemical formula would be (Zn,Fe)S. Sphalerite has a wide color range, depending principally on iron content. Pure to almost pure sphalerite is whitish to greenish. With increasing iron content, sphalerite becomes yellowish to brownish to blackish. One variety of sphalerite has a strikingly intense dark red color (ruby sphalerite). It's streak color also varies with iron content from whitish to pale yellowish to brownish. Sphalerite is also distinctive in being moderately heavy for its size and having six different planes of cleavage.
Sphalerite is the most important zinc ore mineral. Zinc produced from sphalerite is used for many purposes, including mixing with copper to produce brass, rust protection of iron & steel, and for making modern American pennies (although the cost of making each zinc penny is >1¢).
Sphalerite cleavage fragment (3.7 cm across at its widest) from a mine in the Tri-State Mining District, Ottawa County, Oklahoma, USA.
Sphalerite (field of view ~3 cm across)
Sphalerite (black) & barite (whitish-yellow) from the Cumberland Mine, Smith County, Tennessee, USA (CMC RM 1140, Cincinnati Museum Center's rock & mineral collection, Cincinnati, Ohio, USA).