Arsentsumebite , Mimetite Locality: Tsumeb Mine (Tsumcorp Mine), Tsumeb , Otjikoto (Oshikoto) Region, Namibia ( Locality at mindat.org ) Size: 5.6 x 4.3 x 2.9 cm. An exceptionally rare and rich, very old-time specimen. This was originally labeled as pyromorphite (but never checked by analysis). Pyromorphite is not reported in crystalline form of any quality from Tsumeb and this would have been a miraculous piece. Further study has confirmed it is actually arsentsumebite pseudomorph after mimetite. Specimens of this type were reported to have been found in the upper oxidation zone, and so it most likely dates to 75 years or more in age. Ex. Gary Hansen Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Arsentsumebite
Arsentsumebite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Pb₂Cu(AsO₄)(SO₄)(OH).
It crystallizes in the monoclinic crystal system (space group P2_1/m). It is a member of the Brackebuschite structural group.
Key properties: Mohs hardness 3.5; specific gravity 6.46; [Vitreous.] luster; optically biaxial.
IMA symbol Atsu, grandfathered status — known before the IMA’s founding, named in 1935.
A rare mineral found in the oxidized zone of a dolostone-hosted hydrothermal polymetallic ore deposit (Tsumeb, Namibia); in a hydrothermal polymetallic barite–fluorite deposit (Clara mine, Germany).
It is found associated with Malachite, cerussite, azurite, smithsonite, mimetite, bayldonite, conichalcite, duftite, quartz, iron oxide (Tsumeb, Namibia).
As the arsenate analog of tsumebite.