No matter how you slice it, this is an amazing specimen. It is huge, attractive, and mineralogically fascinating. First thought to be a cast of Smithsonite after Calcite, I don't think that is strictly true. Looking at the layering, you can see layers of tan (Smithsonite) and white (Calcite). The striking fluorescent view supports the idea of this piece being Smithsonite ON a Calcite cast, rather than replacing it. It is a 'Horn of Plenty' in every way. Simply outstanding, and better in person.