Hollow crystals of Siderite epimorph after Calcite. Epimorph is a type of pseudomorph where a mineral replaces another mineral and the original mineral dissolves, leaving a hollow cast surrounded by the new mineral. Rich tan Siderite replaces completely scalenohedral Calcite crystals with flat tips. One of the crystals has a hole where the epimorph is very well visible. Sphalerite is present as well. In good condition. On acrylic base.

Neat epimorph!