Pseudojohannite from Jachymov, Musonoi, and La Creusaz: A new member of the zippeite-group

Pseudojohannite is a hydrated copper(II) uranyl sulfate described from Jachymov, Northern Bohemia, Czech Republic (type locality). Pseudojobannite also occurs at the Musondi quarry near Kolwezi, Shaba, Congo, and the La Creusaz prospect, Western Swiss Alps. At all three localities. pseudojohannite formed through the interaction of acid sulfate mine drainage waters with uraninite (Jachymov and La Creusaz) or uranyl silicates (Musondi). Pseudojohannite forms moss green, non UV-fluorescent aggregates consisting of irregularly shaped crystals measuring up to 25 pm in length and displaying an excellent cleavage parallel to (1) over bar 01). d(meas) is 4.31 g/cm(3), d(calc) 4.38 g/cm(3). and the refractive indices are n(min) = 1.725 and n(max) = 1.740. A high-resolution synchrotron powder diffraction pattern on the material from Musondi shows that pseudojohannite is triclinic (P1 or P (1) over bar), with a = 10.027(1) angstrom, b = 10.822(1) angstrom, c = 13.396(1) angstrom, alpha = 87.97(1)degrees, beta = 109.20(1)degrees, gamma = 90.89(1)degrees, V = 1371.9(5) angstrom(3). The location of the uranium and sulfur atoms in the cell was obtained by direct methods using 1807 reflections extracted from the powder diffractogram. Pseudojohannite contains zippeite-type layers oriented parallel to ((1) over bar 01). The empirical chemical formula calculated for a total of 70 0 atoms is Cu6.52U7.85S4.02O70H55.74, leading to the simplified chemical formula Cu-6.5[(UO2)(4)O-4(SO4)(2)](2)(OH)(5)(.)25H(2)O. The distance of 9.16 angstrom between the uranylsulfate sheets in pseudojohannite shows that neighboring layers do not share 0 atoms with the same Cu Phi(6) [Phi = (O,OH)] distorted octahedrons, such as in magnesium-zippeite. Rather, it is expected that Cu Phi(6) forms a layer bound to the zippeite-type layers by hydrogen bonding, as in marecottite, or one apex of the Cu Phi(6)polyhedron only is shared with a zippeite-type layer, as in synthetic SZIPPMg. The higher number of cations in the interlayer of pseudojohannite (Cu:S = 1.6:1) compared to marecottite (3:4) and SZIPPMg (1: 1) indicates that pseudojohannite has a unique interlayer topology. Ab-initio powder structure solution techniques can be used to obtain important structural information on complex micro-crystalline minerals such as those found in the weathering environment. Pseudojohannite represents a new member of the zippeite group of minerals, and further illustrates the structural complexity of zippeite-group minerals containing divalent cations, which have diverse arrangements in the interlayer. Peudojohannite and other divalent zippeites are common, easily overlooked minerals in acid drainage environments around uranium deposits and wastes.