Journal of Geosciences, 54 (2009), 355–371 DOI: 10.3190/jgeosci.055 Original paper Cu-rich members of the beudantite–segnitite series from the Krupka ore district, the Krušné hory Mountains, Czech Republic Jiří SeJkOra1*, Jiří ŠkOvíra2, Jiří ČeJka1, Jakub PláŠIl1 1 Department of Mineralogy and Petrology, National museum, Václavské nám. 68, 115 79 Prague 1, Czech Republic;
[email protected] 2 Martinka, 417 41 Krupka III, Czech Republic * Corresponding author Copper-rich members of the beudantite–segnitite series (belonging to the alunite supergroup) were found at the Krupka deposit, Krušné hory Mountains, Czech Republic. They form yellow-green irregular to botryoidal aggregates up to 5 mm in size. Well-formed trigonal crystals up to 15 μm in length are rare. Chemical analyses revealed elevated Cu contents up 2+ to 0.90 apfu. Comparably high Cu contents were known until now only in the plumbojarosite–beaverite series. The Cu 3+ 3+ 2+ ion enters the B position in the structure of the alunite supergroup minerals via the heterovalent substitution Fe Cu –1→ 3– 2– 3 (AsO4) (SO4) –1 . The unit-cell parameters (space group R-3m) a = 7.3265(7), c = 17.097(2) Å, V = 794.8(1) Å were determined for compositionally relatively homogeneous beudantite (0.35 – 0.60 apfu Cu) with the following average empirical formula: Pb1.00(Fe2.46Cu0.42Al0.13Zn0.01)Σ3.02 [(SO4)0.89(AsO3OH)0.72(AsO4)0.34(PO4)0.05]Σ2.00 [(OH)6.19F0.04]Σ6.23. Interpretation of thermogravimetric and infrared vibrational data is also presented. The Cu-rich members of the beudan- tite–segnitite series are accompanied by mimetite, scorodite, pharmacosiderite, cesàrolite and carminite.