Original paper
Orthowalpurgite (UO2)Bi4O4(AsO4)2-2H2O, a new mineral from the Black Forest, Germany
Krause, Werner; Effenberger, Herta; Brandstätter, Franz
European Journal of Mineralogy Volume 7 Number 6 (1995), p. 1313 - 1324
40 references
published: Dec 22, 1995
manuscript accepted: May 22, 1995
manuscript received: Nov 23, 1994
DOI: 10.1127/ejm/7/6/1313
Abstract
Abstract The new mineral orthowalpurgite was found associated with preisingerite, quartz and anatase on a specimen from the dump of the Schmiedestollen, Wittichen, Black Forest, Germany. It forms transparent, yellow, orthorhombic crystals with 2/m symmetry up to 0.3 mm, tabular II {010}, elongated II [100]; crystallographic forms are {010}, {010}, {104}, and {100}; Mohs' hardness 4½, density(calc) = 6.51 g cm-3. The crystals are brittle, show a conchoidal fracture, and an indistinct cleavage parallel to {001}. Orthowalpurgite is biaxial negative, nx = 1.91(2), ny = 2.00(2) and nz = 2.05 (calculated), 2VX = 70(3)° (λ = 589 nm); orientation: X II c, Y II a, and Z II b. Neither pleochroism nor dispersion were observed. Electron-microprobe analyses gave UO3 17.86 wt.%, Bi2O3 64.21 wt.%, As2O5 16.11 wt.%, H2O (calculated from the idealized formula) 2.43 wt.%, Σ 100.61 wt.%; this yielded the empirical formula (based on 16 oxygen atoms) (UO2)0.92Bi4.06O3.89(AsO4)2.07-1.99H2O, ideally (UO2)Bi4O4(AsO4)2-2H2O. The cell parameters are a = 5.492(1) Å, b = 13.324(2) Å, c = 20.685(3) Å, V = 1513.6 Å3, space group Pbcm, Z = 4. A crystal structure investigation was performed using single-crystal X-ray data. The refinement converged at R = 0.080 and Rw = 0.031 for 999 reflections with sin θ/λ 2α(Fo)] and 68 variable parameters. The coordination polyhedra around the Bi[4+2] and Bi[5+2] atoms are edge- and corner-connected to Bi8O8 layers. The layers are interconnected via (UO2)(AsO4)2 chains to form a three-dimensional network. The name orthowalpurgite was chosen to express the structural relationship to the triclinic polymorph walpurgite
Keywords
orthowalpurgite • (UO2)Bi4O4(AsO4)2-2H2O • new mineral • Wittichen (Black Forest • Germany) • crystal structure • walpurgite