Fig. 2

Mapping of the inked fiber (I). a SEM image of the thin section; b and c STXM maps of a restricted area (yellow square) at the Fe L-edge: b the map at 708 eV (after subtraction of maps at 700 eV) represents Fe^II distributions; c the map at 709.8 eV (after subtraction of maps at 708 eV) represents Fe^III distributions; d RGB picture resulting from fit of the stack with Fe^II (Fig. 1a, yellow) and Fe^III (Fig. 1a, blue) reference spectra. e Regions of interest (from numbers 1 to 3) chosen to extract the NEXAFS spectra shown on Fig. 3a