Fig. 6

⁵⁷Fe Mössbauer spectra of pyrolusite resuspended 1, 2, and 3 times in 3 mM aqueous Fe(II), where the Fe isotope order of addition was ⁵⁷Fe–⁵⁶Fe–⁵⁶Fe. A marked increase in magnetite character can be observed in successive spectra, which is indicative of chemical transformations occurring only in the initial ⁵⁷Fe atoms oxidized and precipitated on the pyrolusite surface. A summary of lepidocrocite and magnetite ratios obtained from fitting of the Mössbauer spectra is available in Table 2