The crystal structure of vauquelinite and the relationships to fornacite

Abstract

Vauquelinite, Pb 2 Cu[CrO 4 PO 4 OH], is monoclinic, with a = 13.754, b = 5.806, c = 9.563 Å, β = 94°34′, space group P 2 1 / n . The crystal analysis of the mineral was determined by the trial-and-error method starting from the atomic positions found in fornacite. The refinement carried out by the least-squares method gave a final discrepancy index R of 0.089. The atomic packing in vauquelinite is very similar to that in fornacite. Some differences occur in coordination around lead ions and in the arrangement of symmetry elements in the two minerals.