Calcite on Dolomite

I purchased this piece in 2004 due to the very subtle yet startlingly beautiful subtle contrast between the pale yellow prismatic calcites and the pearly white dolomite coating ( the photo appears pinkish, but it is not)the typical Tsumeb matrix. A single broken crystal reveals a core that formed over a dark linear crystal that is difficult to identify visually, but I suspect to be a secondary copper mineral. Ex Geoffrey Krasnov collection.

Locality: Tsumeb Mine, Tsumeb, Namibia

Composition: calcium carbonate