57Fe-Mössbauer spectroscopy on natural eosphorite-childrenite-ernstite samples.

Abstract

Samples of the eosphorite-childrenite [(Mn2+, Fe2+)AlPO4(OH)2H2O] series from Divino das Laranjeiras and Araçuaí (Minas Gerais State) and Parelhas (Rio Grande do Norte State) pegmatites have been investigated by X-ray diffraction, microprobe analysis and Mössbauer spectroscopy at 295 and 77 K. The Mössbauer spectra of ernstite [(Mn2+, Fe3+)Al- PO4(OH)2-xOx] showed the existence of ferric ions in both A and B sites, whereas ferrous ions seem to be located exclusively in the A site. Nonoxidised samples show ferrous ions located in both sites, and no Fe3+ could be detected. The interpretation of the Mössbauer spectra of both, oxidised and nonoxidised samples, is difficult because the hyperfine parameters of these minerals are rather similar, rendering it difficult to make proper site assignments.