This isn't an official "mineral," nor is it pure metal: It's the copper that stuck to the fire brick walls of the smelters in copper ore processing plants in Northern Michigan. It's really interesting material: Smooth and glimmery, the copper is studded with either a cream or black mosaic pattern of fire brick chips caught forever in the metal. Most of these smelters are no longer in operation, so each cab contains a little bit of the history of the Upper Midwest. Each piece has the weight of metal, and a patina like antique copper. A really wonderful stone for people who work in, or just love, copper.