Refinement of wulfenite in space group I-4

Acta Cryst. (2011). C67, i33-i35 [ doi:10.1107/S0108270111015769 ]
On the symmetry of wulfenite (Pb[MoO4]) from Mezica (Slovenia)
I. Cora, M. Czugler, I. Dódony and A. Recnik

Abstract: Wulfenite [lead(II) molybdate(VI)] is known as a scheelite structure in the I41/a space group. The structure of the unusual `hemimorphic' wulfenite crystals from the Mezica mine was refined in the noncentrosymmetric space group I\overline{4} using a Pb/Mo exchange disorder model with the approximate composition Pb0.94Mo0.06[MoO4]. Pb atoms in the 2b positions are substituted by Mo at about 12%. The crystal is shown to be twinned by inversion. Hemimorphism may result from the short-range chemical ordering of the metal atoms at the 2b positions.