• finnemanite;
  • paulmooreite;
  • nealite;
  • carfasite;
  • single-crystal Raman spectroscopy;
  • antimonite

The single-crystal Raman spectra of the natural mineral finnemanite Pb5(AsO3)3Cl from the Långban locality, Filipstad district, Värmland province, Sweden, are presented for the first time. It is a hexagonal mineral belonging to the ortho-arsenite group, where the [AsO3]3− ion is isolated. The spectra of finnemanite are characterised by a strong band at 734 cm−1 overlying a shoulder at 726 cm−1, and broad overlapping bands in the lower wavenumber region with the strongest band positioned at 174 cm−1. Band assignments were made on the basis of band symmetry, experimental band positions from the literature, the calculated Raman spectrum using density functional theory and spectral comparison with other ortho-arsenite minerals reinerite, cafarsite and nealite as well as with synthetic lead arsenite compounds Pb2(AsO2)3Cl, Pb2As2O5 and PbAs2O4. The band at 734 cm−1 was assigned to ν1 (AsO3); those at 726 and 640 cm−1 to ν3; those at 372 and 357 cm−1 to ν2, and those at 244, 239 and 207 cm−1 to ν4. The single-crystal spectra of finnemanite showed good mode separation, allowing the bands to be assigned to the symmetry species Ag, E1g or E2g. Copyright © 2011 John Wiley & Sons, Ltd.