Manganoan rockbridgeite Fe4.32Mn0.62Zn0.06(PO4)3(OH)5:: structure analysis and 57Fe Mossbauer spectroscopy

The structure of the basic iron phosphate rockbridgeite [ iron manganese zinc tris( phosphate) pentahydroxide] was reinvestigated with special emphasis on the cation distribution deduced from new X-ray and Fe-57 Mossbauer data. Rockbridgeite is orthorhombic, space group Cmcm, and shows three different Fe sites, one with 2/m symmetry, another with m symmetry and the third in a general position. One phosphate group has the P atom on a site with m symmetry, while the other has the P atom at a site with mm symmetry. Two Fe sites are fully occupied by ferric iron, while Mn3+ and Fe2+ are situated at a third, principally Fe, site. Structural data, bond-valence sums and polyhedral distortion parameters suggest a new interpretation of the rockbridgeite Fe-57 Mossbauer spectrum.