Chemistry: [Ca2(H2O)17Ca(H2O)6][Mo8As2Fe3+3O36(OH)]
Size: 55 mm
Owner: W.W. (Bill) Pinch
Photographer: Jeff Scovil

This remarkable specimen was collected by John Innes, the chief mineralogist at Tsumeb, on 13 May, 1983, from the second oxidation zone.  It consists mainly of massive, bright yellow, micro-crystalline betpakdalite-CaCa, and was one of the specimens studied for the characterisation of the heteropolymolybdate family of minerals, in which betpakdalite-CaCa and betpakdalite-CaMg were recognised as distinct species (Kampf et al., 2012). Tiny crystals of scorodite are present on the back of the specimen, although these are not apparent from this photograph.