X-ray diffraction, infrared and Moessbauer studies of Fe-rich carbonates

XRD data indicate a clear variation in unit-cell parameters with composition for siderites and Fe-rich members of the dolomite- ankerite series, although carbonates near to pure siderite show some scattering. IR spectroscopy shows small shifts (< 10 cm (super - 1) ) in the three vibrational frequencies 1420, 870 and 730 cm (super - 1) ; the relationship between composition and the 870 and 730 cm (super -1) bands is approximately linear for siderites but non- linear for ankerites. Mossbauer data reveal the presence of one unique type of site occupancy as well as distortion in FeO (sub 6) octahedra in siderites. Quadrupole splitting and Fe content seem to be independent from each other, but there is some correlation between the amount of Fe and the area of the band exists. The variation for compositions close to pure siderite may be due to the antagonistic effect caused by substitution of Ca and Mg for Fe in octahedral sites.