Luanheite: Elisa de Bordos Mine, Northern Chile. (Connoisseur's Choices).

A wise man once said, "All that glitters is not gold." Well, all dense, metallic silver-gray, arborescent crystalline masses in calcite are not always silver, either. They could be luanheite, a mineral unfamiliar to virtually all of us, but from whose discovery, identification, and interesting geochemistry a number' of important lessons can be learned. What is thought to be the finest-known specimen of this incredibly rare, though currently available, mineral was suggested for this column by Ed Huskinson and Matthias Jurgeit.

As the introductory comments suggest and the…