You have found a strange nugget of a metal unknown to you, lodged inside what appeared to be a natural cavity or gas bubble in the lode you were mining. As you examine it, it appears to shimmer as its jagged surface catches the light. You can only imagine the natural processes involved in its creation, but you may be able to find someone who can tell you more.
Fascinating! You found this where? Really now? I don't think I've ever seen anything like this before... I'll need some time to study it, check my notes, maybe consult with a couple of old friends, but I'm certain we have found something amazing here!