Gabrielsonite revisited: crystal-structure determination and redefinition of chemical formula

A reinvestigation of gabrielsonite from the holotype specimen from Långban, central Sweden, using single-crystal synchrotron X-ray diffraction, electron-microprobe techniques and Fourier-transform infrared (FTIR) spectroscopy, Raman and Mössbauer spectroscopies show that the mineral is an anhydrous Fe³⁺-bearing arsenite and not a hydrous Fe²⁺-bearing arsenate, as originally proposed. The revised ideal chemical formula of gabrielsonite is PbFe³⁺(As³⁺O₃)O. The mineral is related to the descloizite supergroup, but it differs through the valencies of the non-Pb cations Fe (M³⁺vs. M²⁺) and As (3 + vs. 4 +) and through lower coordination of Pb (4 vs. 7–8) and As (3 vs. 4). The redefinition of gabrielsonite (proposal 17-G) has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association.