Abstract
A multi-methodological study was conducted in order to provide further insight into the structural and compositional complexity of rare earth element (REE) fluorcarbonates, with particular attention to their correct assignment to a mineral species. Polycrystals from La Pita Mine, Municipality de Maripí, Boyacá Department, Colombia, show syntaxic intergrowth of parisite-(Ce) with röntgenite-(Ce) and a phase which is assigned to B (3) S (4) (i.e., bastnäsite-3-synchisite-4; still unnamed) fluorcarbonate. Transmission electron microscope (TEM) images reveal well-ordered stacking patterns of two monoclinic polytypes of parisite-(Ce) as well as heavily disordered layer sequences with varying lattice fringe spacings. The crystal structure refinement from single crystal X-ray diffraction data - impeded by twinning, complex stacking patterns, sequential and compositional faults - indicates that the dominant parisite-(Ce) polytype M (1) has space group Cc. Parisite-(Ce), the B (3) S (4) phase and röntgenite-(Ce) show different BSE intensities from high to low. Raman spectroscopic analyses of parisite-(Ce), the B (3) S (4) phase and röntgenite-(Ce) reveal different intensity ratios of the three symmetric CO(3) stretching bands at around 1100 cm(-1). We propose to non-destructively differentiate parisite-(Ce) and röntgenite-(Ce) by their 1092 cm(-1) / 1081 cm(-1) ν(1)(CO(3)) band height ratio.