FE-57 MOSSBAUER INVESTIGATIONS OF MANGANESE-CONTAINING SPINELS

Cation distributions and related order-disorder phenomena in the naturally occurring Mn-spinels: iwakiite, galaxite and franklinite, have been investigated by means of Fe-57 Mossbauer spectroscopy. Previous measurements on an iwakiite sample indicated the existence of Mn-rich and Mn-poor regions. This interpretation has been confirmed in this investigation by further measurements on annealed iwakiite samples. The 57Fe Mossbauer spectrum of galaxite from Bald Knob, NC, is a well-resolved quadrupole doublet and indicates the presence of a single crystallographic Fe3+ species. A ''galaxite'' sample from Thailand exhibited a complex spectrum of Fe2+ and Fe3+ quadrupole doublets: This sample has been misidentified and should be regarded as a member of the (Mg, Fe)(Al, Fe)(2)O-4 series. The Fe-57 hyperfine parameters of a rare franklinite from Langban, Sweden, are very close to those for synthetic zinc ferrite, confirming electron microprobe results of an unusually high zinc content.