MÖssbauer spectroscopy of synthetic and naturally occurring staurolite Available to Purchase

Room temperature Mössbauer spectroscopic measurements of 23 natural and 12 synthetic staurolite samples, the latter representing both Fe-Mg and Fe-Li solutions, demonstrate that the majority of the Fe in all samples is Fe²⁺ which occupies the Fe1, Fe2, and Fe3 subsites of the tetrahedral Fe site in an average ratio of 43/12/27. This model is consistent with the H content of the samples where it is known. Additional Fe²⁺ occupancy averaging 11% of Fe_tot in the sample occurs in some combination of the Al(3A), Al(3B), U(1), and U(2) octahedral sites. Some ^[4]Fe³⁺ (averaging 5% in natural and 8% in synthetic samples) is also present, probably replacing Al in the Si site. A poorly resolved doublet with a mean isomer shift of 0.89 mm/s (9% of Fe_tot), possibly representing a charge transfer doublet, is also observed in approximately half the samples. Mössbauer parameters of the various sites do not vary systematically with composition and appear to be independent of next nearest neighbor effects (except in the case of H). These results corroborate previous structure refinement data on the existence of three major Fe subsites and provide direct evidence of minor Fe occupancy in the octahedral sites.