Azurite, (w. Dioptase)

Mineral: Azurite
Chemistry: Cu3(CO3)2(OH)2
Size: 50 mm
Owner: Mark Feinglos
Photographer: Jeff Scovil

Azurite and dioptase are both common minerals at Tsumeb, but they almost never occur in the same paragenesis. Here, terminated, but slightly etched, crystals of blue-black azurite (to 24 mm) are associated with later-formed crystals of emerald-green dioptase (to 2 mm).

This specimen was originally in the collection of Scott Williams (in the late 1950s).  In 1960 it was sold by dealer Martin Ehrmann to the Smithsonian, where it was catalogued as "azurite with tsumebite etc." and assigned USNM # 114693 (see label).  It was subsequently acquired by Walt Lidstrom (see label) by which time the emerald-green mineral had been correctly identified as dioptase. Lidstrom sold the specimen to W.W. (Bill) Pinch, who confirmed the dioptase by analysis. 

The juxtaposition of azurite and dioptase makes this a very important specimen, as remarkably few examples of this paragenesis are known, either from Tsumeb or from any other localities at which the two minerals occur.  At Tsumeb, dioptase is a common mineral in the second oxidation zone, but its occurrence in the first oxidation zone is questionable. Conversely, azurite is abundant in the first oxidation zone but relatively scarce in the second. The provenance of this specimen can be traced back to the late 1950s, shortly after mining operations had penetrated the second oxidation zone and, on balance, it seems likely that this specimen is from the upper part of the second oxidation zone.