Crystal chemistry and miscibility of chernovite-(Y), xenotime-(Y), gasparite-(Ce) and monazite-(Ce) from Mt. Cervandone, Western Alps, Italy

Abstract The crystal chemistry and structure of the rare earth element phosphates, monazite-(Ce), Ce(PO 4 ), xenotime-(Y), Y(PO as well arsenates, gasparite-(Ce), Ce(AsO chernovite-(Y), Y(AsO from hydrothermal quartz-bearing fissures, related to pegmatites overprinted by amphibolite facies, cropping out at Mt. Cervandone, Western Alps, Piedmont, Italy, have been investigated means electron microprobe analysis in wavelength dispersion mode single-crystal X-ray diffraction. chemical data reveal occurrence a full solid solution among isostructural chernovite-(Y) xenotime-(Y) with tetragonal symmetry, whereas wide miscibility gap is observed for gasparite-(Ce) monazite-(Ce) monoclinic symmetry. A significant heterogeneity has several samples, especially Th content, which locally enriched ThSiO grains. refined structural models demonstrates control played composition tetrahedrally-coordinated (As,P)-bearing sites on bulk unit-cell volume, size shape (REE)-coordination polyhedra.