Sphalerite. Credit: Mineral Information Institute.
Sphalerite, also known as zinc blende, is the low-temperature (β) form of zinc sulfide (ZnS). It is the chief ore of zinc, occurring worldwide with galena. Sphalerite forms lustrous, cubic system tetrahedral crystals or granular masses. It is white when pure, but more commonly yellow, black, or brown with a resinous luster. It is often found in hydrothermal veins with galena, and in limestones where it occurs by replacement. Hardness 3.5–4; relative density 4.