Cu-rich members of the beudantite-segnitite series from the Krupka ore district, the Krušné hory Mountains, Czech Republic
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 to 0.90 apfu. Comparably high Cu contents were known until now only in the plumbojarosite-beaverite series. The Cu2+ ion enters the B3+ position in the structure of the alunite supergroup minerals via the heterovalent substitution Fe3+Cu2+-1 (AsO4)3-(SO4)2--1 . The unit-cell parameters (space group R-3m) a = 7.3265(7), c = 17.097(2) Å, V = 794.8(1) Å3 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)Ε3.02 [(SO4)0.89(AsO3OH)0.72(AsO4)0.34(PO4)0.05]Ε2.00 [(OH)6.19F0.04]Ε6.23 .
Interpretation of thermogravimetric and infrared vibrational data is also presented. The Cu-rich members of the beudantite-segnitite series are accompanied by mimetite, scorodite, pharmacosiderite, cesàrolite and carminite. These minerals are characterised by refined unit-cell parameters and by quantitative chemical analyses. The assemblage of supergene minerals corresponds to the following crystallization sequence: mimetite → beudantite-segnitite → pharmacosiderite, scorodite, cesàrolite, and carminite.
SNIP (Scopus, 2017): 1.120
IF (ISI, 2017): 1.415
5 YEAR IF (ISI, 2017): 1.738
Policy: Open Access