Siderite is not normally a species I go crazy over, but this sharp crystal from an apparently old find in Brazil really is something special. It looks more like a sphalerite than a siderite, and it is one of the few examples of this species in thumbnail size that I think really "stands above" and fits in a superb thumbnail collection. Old piece, ex Rocksmiths from the 1980s, via the Jim Maple collection of Houston. Joe Budd Photos.