Crystal structure refinement of duftite, PbCu(AsO4)(OH), from Grube Clara, Oberwolfach, Schwarzwald, Germany

The crystal structure of duftite, PbCu(AsO4)(OH), has been re-evaluated on the basis of X-ray diffraction data from a single crystal from Grube Clara, Germany. Duftite is orthorhombic with a=7.7668(4),b= 9.2005(5), c= 5.9878(3) angstrom; V=427.88(4) angstrom(3), non-centrosymmetric space group P2(1)2(1)2(1), Z=4. The structure refinement converges to a final R1 value of 0.0174 for 1252 reflections and allows an accurate description of the crystallographic features. The results obtained on the natural sample are compared with those available in the literature for this phase, regarding its synthetic counterpart. The crystal structure of duftite is confirmed and this work reports the first full anisotropic crystal structure refinement for this mineral, with the position of the hydrogen atom determined from the final Delta F map. Duftite is a member of the adelite-descloizite group with the Cu2+ Jahn-Teller active cation in distorted octahedral coordination. Individual bond lengths and other geometrical parameters are compared with those of other arsenates of this group.