A solid mass of very heavy, metallic ore is host for sharp crystals of smaltite, the cobalt-rich variety of skutterudite. Classic old material! This is a good display piece with crystals to 4 mm including a sharp cube, atop. I have chosen not to clean this piece of its acucmulated patina, though it is of course easy to make it cleaner and bright-looking with chemicals. Note the attractive wavy growths of native bismuth, on which the crystals sit.