Fig. 7
From: Fe(II) reduction of pyrolusite (β-MnO2) and secondary mineral evolution
Relative abundances of lepidocrocite (open markers) and magnetite (closed markers) in marginal Fe(II) additions, as determined by Mössbauer spectral fitting of 57Fe phases at 77 K. Experiments were only exposed to 57Fe during the final Fe(II) resuspension, permitting us to view chemical changes occurring to the marginal Fe(II) addition. After initial reaction of pyrolusite with 3 mM 57Fe(II), only lepidocrocite was detectable in Mössbauer spectra. Increasing 56Fe(II) exposure prior to final 57Fe(II) exposure resulted in marginal 57Fe precipitate formation increasingly dominated by magnetite, as identified by characteristic overlapping sextets in Mössbauer spectra