2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 5
Presentation Time: 1:30 PM-5:30 PM


SCHAEFER, Martha W., Dept. of Geology and Geophysics E235 Howe-Russell, Louisiana State University, E235 Howe-Russell, Baton Rouge, LA 70803 and DYAR, M. Darby, Dept. of Earth & Environment, Mount Holyoke College, South Hadley, MA 01075, schaefer@geol.lsu.edu

Mössbauer spectroscopy is a valuable technique to determine ferric/ferrous ratios and site occupancies in iron-bearing minerals. However, Mössbauer spectra of minerals frequently exhibit highly-overlapping peaks, and under these conditions the particular fitting techniques and model assumptions used can affect how the spectra are interpreted. We examine here a small number of well-characterized (with respect to both site occupancy and ferric/ferrous ratio) mineral samples and analyze their Mössbauer spectra with four popular Mössbauer spectral analysis programs to determine the degree of agreement between the results. Typically, members of a research group will use only one of these spectral analysis programs, and differences in interpretation that might arise from the use of different programs are therefore virtually unknown. In addition, there are many physical models that have been applied to interpret Mössbauer spectra, and there have been few published comparisons of any of these models. It is hoped that this study will enable Mössbauer spectroscopists to correctly compare results from different research groups, and also to make informed choices for using the software that best fits their data. Preliminary results of our ongoing study to compare these four programs highlight the necessity for intelligent and thoughtful fitting of Mössbauer spectra. It is possible to produces fits of the same, relatively simple spectrum, with similar chi-squared values but significantly different Mössbauer parameters or even numbers of peaks, and these results can be highly variable not only between programs but while fitting with one program alone. Clearly more work must be done to determine the causes of this variability and the best methods of interpreting these results. This is important not just to the interpretation of present and future spectra, but to the understanding of spectra and Mössbauer parameters in the literature.