From a small find that was brought out at Munich, these are specimens I bought there at the show in 2006 but only got a hold of in a shipment back to me at the Tucson Show the following February. These are very unusual crystals in that they are hollow casts after calcite, and the coating is a true mixture of sphalerite and siderite (almost an amalgam?!) They have been extensively analyzed in South Africa, to come up with this conclusion. So far as I am aware, this is a first. I selected just a few specimens on the run at Munich with regards to getting pieces with superior 3-dimensional form, a good surface shimmer (almost metallic!), and no damage. I think these pieces were, from what I saw, among the best for quality that could be had. This specimen is one of the better clusters I saw, for the size, and has a wonderful surface sheen and shimmer to it, much more evident and almost golden, in person!