Collection and Analysis of High Temperature-Resolution 57Fe Mössbauer Spectroscopy for Detailed Iron Mineral Characterisation.

57Fe Mössbauer spectroscopy is a powerful technique for determining the oxidation state and magnetic properties of Fe-bearing materials. Since magnetic properties are temperature dependent, Mössbauer spectra are often collected at multiple temperatures, especially around characteristic transition points such as the magnetic blocking temperature. Mössbauer data acquisition times are slow, sometimes taking >24 h to achieve high signal-to-noise ratios (SNR), which limits the number of spectra that can be collected. Here we propose an alternative approach, measuring profiles with high temperature resolution (e.g. 1 K temperature steps) but lower SNR. Using ferrihydrite with varying crystallinity as examples, we revealed mineralogical properties with increased detail even without large increases in the total acquisition time. The temperature dependence of the hyperfine parameters was clearly revealed in qualitative analysis, while simultaneous quantitative analysis of the spectra in both the temperature and energy domains revealed details about the distribution of particle crystallinity in pure ferrihydrite and mixed-phase samples. This approach will improve the measurement of temperature-dependent mineral properties, enabling analysis of blocking temperature distributions, improving the interpolation of hyperfine parameters in temperature profiles and aiding the discrimination of overlapping spectra in mixed-phase samples.