SPHALERITE
purple fluorite almost covers this specimen of ruby jack sphalerite - specimen from the Elmwood mine, Tennessee (actual colour - most like the bottom picture)
ZnS. Zinc Sulfide
Sphalerite is the principal ore of zinc, and is also known as "blende". The name is from the Greek word "sphaleros", meaning "treacherous" - probably because of similarity to several other minerals. It is usually very dark brown to black in colour, but, occasionally, transparent yellowish brown or green stones are found that can be faceted. The crystals are usually pseudo-octahedra in shape, forming in hydrothermal veins with other minerals, such as galena, quartz, pyrite and calcite.
Hardness: 3 1/2 - 4