Original paper

Schlegelite, Bi7O4(MoO4)2(AsO4)3, a new mineral from Schneeberg, Saxony, Germany

Krause, Werner; Bernhardt, Heinz-Jürgen; Effenberger, Herta

Abstract

Schlegelite is a new bismuth molybdate arsenate from the dumps of the Pucher Richtschacht, near Schneeberg, Saxony, Germany. Associated minerals are quartz, petitjeanite, pucherite, bismuth and sillenite. Schlegelite forms dense spherical aggregates that are composed of small lath-like crystals up to 0.3 mm in length. Crystallographic forms are {010} (dominant), {001} and {100}; the elongation is parallel to [100]. The colour is yellow, the streak is pale yellow; Vickers hardness is VHN25 = 285 kg/mm2, corresponding to a Mohs' hardness of 31/2; good cleavage parallel to {010} and {001}. Schlegelite is biaxial negative, 2V = 40(5)°, nx = 2.22, ny = 2.255 (calc.), and nz = 2.26 (calculated from reflectance data); non-pleochroic; orientation X = a, Y = b, Z = c. Electron-microprobe analyses gave Bi2O3 70.20, PbO 0.48, CaO 0.05, P2O5 0.51, As2O5 15.38, V2O5 0.21, MoO3 12.13, total 98.96 wt.-%. The empirical formula based on 24 oxygen atoms is Bi6.78Pb0.05Ca0.02O3.51(MoO4)1.90(PO4)0.16(VO4)0.05(AsO4)3.01, the idealized formula is Bi7O4(MoO4)2(AsO4)3. Schlegelite is orthorhombic, space group Pnca, with a = 5.299(1), b = 16.133(4), c = 23.948(5) Å, V = 2047.2(7) Å 3 , Z = 4, Dcalc = 7.23 g/cm3. The crystal structure refinement converged for 2378 reflections and 166 variable parameters at R1 = 0.045. The atomic arrangement is characterized by ribbons of Bi atoms shortly linked by oxo-oxygen atoms parallel to [100]. The ribbons are connected to AsO4 and MoO4 tetrahedra forming layers parallel to (001). The chemical composition of schlegelite is remarkable as minerals containing both the anion groups, arsenate and molybdate, are rare; furthermore, Bi arsenates with a second anion group were found only occasionally. The mineral name is for Fritz Schlegel, a dedicated mineral collector and finder of the new species, in recognition of his contributions to the mineral assemblage of the Schneeberg area in Saxony, Germany.

Keywords

schlegeliteschneeberggermanynew mineralmicroprobe analysiscrystal chemistrycrystal structure