Duhamelite discredited

Reinvestigation of duhamelite, originally described as Cu4Pb2Bi(VO4)(4)(OH)(3) . 8H(2)O, has demonstrated that it is not a valid independent mineral species. Analyses of the type material and of additional samples by means of electron microprobe, X-ray powder and single-crystal diffractometry including structure refinements, and transmission electron microscopy have shown that duhamelite belongs to the adelite-descloizite-group with the general formula AB(XO4)(OH). Duhamelite in the strict sense corresponds to a bismuth- and calcium-bearing mottramite; the empirical formula of the type material is (Pb0.49Bi0.36Ca0.12)(Sigma0.97)Cu-1.0[(VO4)(0.85) (AsO4)(0.08)(SiO4)(0.07)](Sigma1.00)[O-0.27(OH)(0.71)](Sigma0.98) (based on 5 oxygen atoms per formula unit), or simplified (Pb,Bi,Ca)Cu(VO4)(OH,O). The formal discreditation of duhamelite has been approved by the Commission on New Minerals and Mineral Names, I.M.A.