A multi-analytical approach using electron microprobe analysis, X-ray structural refinement, and polarized single-crystal Fourier transform infrared spectroscopy was used to characterize short-range and long-range structures of a Pb2+-bearing, Mn3+-rich pargasite. Site populations, derived from the results of site-scattering refinement and stereochemical analysis, demonstrate that Pb2+ is strongly ordered at the A-site in the monoclinic C2/m amphibole structure. This finding is in agreement with the observed ordering of Pb2+ in the rare Pb2+-bearing P2/a amphibole joesmithite, but is in contrast to a Pb2+ preference for the M4 site suggested by some studies on element partitioning between C2/m amphiboles and melts. Mn3+ is strongly ordered at the M2 site in structure of the present amphibole. Contrasting results obtained for mean M2-O bond lengths and reported local Mn3+-O bond lengths as well as between bond-length distortion of the mean M2 polyhedron and the local Mn3+-centered M2O6 octahedron in pargasite indicates that the structural relaxation of this polyhedron is complete or nearly so.

You do not have access to this content, please speak to your institutional administrator if you feel you should have access.