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Arsentsumebite, (after Mimetite)


Size: 95 mm
Owner: Paul Melville
Photographer: Paul Melville

Prismatic, hexagonal pseudomorphs of arsentsumebite after mimetite, on a matrix that is also rich in arsentsumebite (?), possibly in association with other copper arsenates (?).The replacement of the original mimetite is incomplete, as shown by cores of residual mimetite in the one or two broken crystals on the specimen.

 
 
 
 
 
 
 
 

Accessory azurite is present in vugs and fractures, and one small group of azurite crystals (lower right of centre in the main photograph) has been replaced by malachite. Small glassy crystals of cerussite (to 1 mm) are widely distributed on the matrix, though difficult to see in these images.

The specimen has an interesting provenance, in that the accompanying label (erroneously identifying the specimen as bayldonite after mimetite) is from the Viktor Hoffmann  (Berlin) collection and the handwritten note on the back of the label indicates that it was purchased from former OMEG general manager, Wilhelm Thometzek, in 1932, for 5.00 marks. A later (?) handwritten note reads "Para aurichalcit", which was a name given to ill-defined botryoidal crusts and earthy materials formed by the action of zinc-bearing solutions on malachite-rich material at Tsumeb; often a mixture of malachite and rosasite (www.mindat.org).