Using Electron Paramagnetic Resonance spectroscopy One approach to assess the redox properties of manganese in a sample has focused on electron paramagnetic resonance (EPR) spectroscopy. EPR is an extremely sensitive technique to measure molecules with unpaired electrons (including Mn(II) and Mn(IV) species), and it has been useful for understanding the electronic structure and redox states of Mn in biochemical systems (see More et al., 1999; McEvoy and Brudvig, 2006). However, when this technique is applied to geological samples, results can become more complicated and nonunique. From observations of particularly narrow EPR line widths, it was suggested that EPR could be useful for distinguishing the biogenicity of the oxides (Kim et al., 2011). Yet in concentrated geological samples, dipole-dipole interactions between closely packed Mn atoms affect the EPR signals (Pingitore et al., 1988). Thus, when Mn is concentrated in samples, it is difficult to distinguish Mn(II) minerals like rhodochrosite (MnCO3) from Mn(III) or Mn(IV) minerals (Pingitore et al., 1988). Furthermore, EPR of samples is effectively a bulk measurement that requires sample homogenization and thus does not pair redox data to mineral textures.