MOSSBAUER SPECTROSCOPIC STUDY OF SYNTHETIC LIPSCOMBITE AND BARBOSALITE AT ROOM-TEMPERATURE

Barbosalite and lipscombite hydroxyphosphates have been prepared and c haracterized by Mossbauer spectroscopy. These phases have been shown t o be constituted of chains of Fe-oxygen octahedra sharing faces. The p rincipal difference in the arrangement of the ions in these structures is the organization of the octahedra in the chains. In barbosalite, t he chains are composed only of trimeric groups (Fe3O12) separated by a vacant octahedral site, while lipscombite chains are composed of grou ps of (2n + 1) iron cations, n varying from 0 to 5 or 6. The relative abundance of the different groups was calculated from published X-ray diffraction data and used to attribute the three ferric and the two fe rrous doublets observed in the Mossbauer spectrum of lipscombite. This attribution is confirmed by the comparison with the results obtained on barbosalite.