These are mirror-bright, sharp crystals of skutterudite.
From the mine that has produced the world’s finest crystals of skutterudite, this specimen is largely free of the usual problem with these – they grow in small calcite-filled vugs and are typically heavily intergrown, with little space for crystal growth. As a result, most specimens one sees have contacts and incomplete crystals all over. This piece features a knob of crystals largely independent of the surrounding host rock, with only a contact at the right that I would display angled towards the back, away from view. The crystals are in excellent condition – no damage.
A great high-quality specimen of skutterudite.