Arsentsumebite pseudo after Mimetite
Tsumeb Mine, Tsumeb, Oshikoto Region, Namibia
Miniature, 3.9 x 2.7 x 2.8 cm

A sharp cluster of this very rare pseudomorph of Arsentsumebite after Mimetite, found only at Tsumeb long ago. These specimens were found only in the oldest, upper oxidation zone of Tsumeb (prior to WWI, generally). The pseudomorphed crystals are in a divergent group and vary in length from just under one centimeter to 2.2cm. Some of the crystals are hollow (or hoppered?) as evident from looking down the long axis. The piece has a rich, variegated green-yellow to yellow-green color to it, and a very three-dimensional aspect to make it aesthetic. One crystal that is nicked at the termination reveals an internal turquoise blue color (posnjakite perhaps?), another imperfection near the base of that same crystal exposes a small glassy area of primary Mimetite! A different incomplete crystal near the base at the periphery shows a similar feature with a core of Mimetite and a rim of Arsentsumebite. The piece has an earthy luster to it as most of these singular pseudomorphs do. Some have remarked that the replacement is a mix of Arsentsumebite and Bayldonite, despite the traditional labeling as Bayldonite replacements; we have not had this analyzed to determine what the replacement mineral(s) is/are. You can assume it may be a mix of those species, although the arsentsumebite replacements I have seen per label tend to be lighter; and bayldonite does tend to be darker in documented examples we have seen. It is, in any case, exceedingly difficult to find a good example of this old material and this three-dimensional, rare and excellent old-time piece is unusually display-worthy!

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