Fig. 8

⁵⁷Fe Mössbauer spectra of all experimental data collected in which only the final resuspension of Mn particles was done using ⁵⁷Fe(II). Room temperature (RT, 298 K) spectra are provided for all experiments (left column), with selected 77 K spectra of identical experiments (right column) for comparison. After only one resuspension in 3 mM Fe(II), the resulting spectrum is devoid of multi-sextet character typical of magnetite. As the amount of Fe(II) exposure increases, we can see the final deposition of ⁵⁷Fe atoms onto the particle surface results in an increasingly large multi-sextet signal and a gradual disappearance of the doublet associated with lepidocrocite formation. Comparing RT spectra with 77 K, magnetite sextets appear to overlap more thoroughly at 77 K, which is commonly observed below the Verwey transition temperature (~ 120 K). Spectra collected at 77 K also contain a visibly higher ratio of sextet: doublet spectral area, possibly indicating the presence of unordered magnetite at room temperature, which orders into a typical sextet at lower collection temperatures