This pseudomorph of Smithsonite after Calcite is from the well-known 19th Century production at the Mineral Point copper deposits in this old mining district, though very few specimens were preserved and fewer still turn up on the modern market. In these specimens, Smithsonite has pseudomorphed a cluster of Calcite crystals, with the largest of these crystals being 3 cm on edge. Greenockite, a cadmium sulfide, has covered the crystals, imparting a strong, burnt-orange color. This is a famous old occurrence and specimens are rare today, particularly good larger-sized pieces such as this one.