Acta Musei Moraviae

Demesmaekerite from uranium deposit Zálesí in the Rychlebské hory Mts. (Czech Republic)

A rare secondary mineral demesmaekerite Pb₂Cu₅(SeO₃)₆(UO₂)₂(OH)₆ . 2H₂O was newly found on the old dumps of Pavel vein at the abandoned uranium deposit of Zálesí in Rychlebské hory Mts. Demesmaekerite forms light green compact aggregates up to 1 mm large, in cavities also tabular crystals with vitreous lustre, up to 0.05 mm in size. It commonly forms intergrowths with deep blue chalcomenite. The XRD data of demesmaekerite together with the chemical composition of demesmaekerite and chalcomenite are given. Both minerals represent the decomposition product of clausthalite, uraninite and chalkopyrite. Demesmaekerite is very rare secondary mineral and Zálesí represents its second world occurrence.