Arsentsumebite, (after Mimetite)

Size: 40 mm
Owner: Mariusz Oleszczuk
Photographer: Mariusz Oleszczuk

A large and sculptural example of arsentsumebite pseudomorphous after mimetite, believed to have been collected from high in the first oxidation zone, early in the 1900s, when similar replacements were found in some abundance.  

At that time, these were thought to be pseudomorphs of bayldonite after mimetite, but modern analysis shows that the majority of them are, in fact, arsentsumebite.  XRD analysis of this particular specimen, however, has shown that the replacing arsenate is a mixture of arsentsumebite with minor bayldonite.

Small darker green pseudomorphs of malachite after azurite adorn the right-hand side of the specimen as seen in the photograph.

Tsumeb is the type locality for arsentsumebite.