Chemistry: Pb2Cu(AsO4)(SO4)(OH)
Size: 60 mm; see scale bars on images
Owner: W.W. (Bill) Pinch
Photographer: RRUFF Project

Arsentsumebite is a common mineral in the first oxidation zone at Tsumeb, although it generally occurs as powdery crusts or micro-crystalline aggregates, and very rarely as distinct, single crystals. The photomicrograph shows well-formed, single crystals of arsentsumebite (to 0.75 mm; verified by single crystal XRD and chemical analysis).  The second photograph shows that the matrix is goethite-rich, and that a little blue linarite is associated with the arsentsumebite.

Tsumeb is the type locality for arsentsumebite, but the mineral has a confused history.  It was first described by Vésignié (1935), who chanced on the correct formula, but was actually working with a mixture of duftite and bayldonite.  Bideaux et al. (1966) described the species in its own right some 30 years later, but the IMA lists the mineral as "Grandfathered", with a 1935 discovery year.

Image courtesy of RRUFF; http//