Dark and shiny. The photograph shows sphalerite crystals, but they are the dark lumps, NOT the small white quartz crystal.
Sphalerite looks similar to galena, hence its name. Originally miners thought that sphalerite was useless, before it was discovered that it is a rich zinc ore.
Larger pictures of Sphalerite:
Natural crystals of sphalerite, and one crystal of quartz.
