Siderite/Sphalerite cast after Calcite

Item Description

From a small find that was brought out at Munich in 2006, these are VERY unusual crystals in that they are hollow casts after calcite, and the coating is a mixture of sphalerite and siderite (almost a true amalgam?!). They have been extensively analysed in South Africa, to come up with this conclusion, by Bruce Cairncross and othres. So far as I am aware, this is a first. This has good 3-dimensional form, a good surface shimmer (almost metallic!), and no damage except to the periphery where you can see into the hollow casts.