Arsentsumebite, (after Azurite)

Size: 85 mm
Owner: Paul Melville
Photographer: Paul Melville

This specimen was originally in the collection of Carl Bosch (1874-1940), which was sold to the Smithsonian in 1966. The USNM label (# B17845) states that the specimen was x-rayed and catalogued as tsumebite.  In fact, the apple-green mineral is arsentsumebite, and it is pseudomorphous after what appear to have been azurite crystals (to 20 mm).

One of the old labels (Frech Minerals) suggests that the pseudomorph could be after anglesite.  Such replacements are recorded from Tsumeb, although the replacement of anglesite by arsentsumebite is rare. In this case, the presence of some residual azurite (at top left in the main photo) supports the view that the arsentsumebite has replaced azurite. A few glassy cerussite crystals are also present.  The specimen is from the first oxidation zone.  (FOV in the close-up photo is approximately 60 mm.)