thometzekite (w. anglesite)

A rich encrustation of pale spearmint-green thometzekite (XRD-verified; Exhibit 2) with blocky, colourless-white crystals of anglesite (to 30mm), lining a vug in oxidising, galena-rich massive sulphide. Under magnification, poorly-defined inclusions of a lime-green mineral are seen, quite abundant close to the junction between the thometzekite and the sulphide. Based on analysis of similar material at the NHM, London, these are likely to be arsentsumebite (Mike Rumsey, pers. comm. to M. Southwood, February 2021).

The specimen was purchased from Ian Bruce in 2015. It was originally in the collection of John Innes, chief mineralogist at Tsumeb in the 1980s and co-discoverer of thometzekite. After Innes' death it passed to Blair Gartrell (Westaus Mineral Museum; # 11321), and thence to Rob Sielecki and later to Ian Bruce. This is specimen JI-426 in the E.H. Nickel catalogue of the Innes collection, although both the Nickel catalogue description and the Gartrell label (Exhibit 3) mis-identify the anglesite as cerussite.

While the location in the mine is not recorded, the paragenesis is strongly indicative of the second oxidation zone.

anglesite; arsentsumebite (?); galena