To quantify hematite nanorod' chemistry, we used the spectra in Fig. as references and convert them into OD1 units, i.e. OD per 1 nm of material at its standard density . To this purpose we used the best fits of the atomic continuum (red solid curves in Fig. ) and then normalized the experimental spectra to the extracted thickness. Density values of 5.3 g/cm 3 for hematite, and 1.82 g/cm 3 for hexahydrate iron chloride were used. Thus, the spectrum in OD1 units for hematite was obtained by dividing the experimental spectrum by 24, while the OD1 spectrum of hexahydrate iron chloride one was obtained by dividing the experimental spectrum by 62. We then applied the SVD (Singular Value Decomposition) method implemented in aXis2000 to the STXM hyperspectral data using these reference spectra to obtain a quantitative chemical mapping, i.e. spatial distribution of the two spectral components. Figure shows the result of the SVD with the two main components being the spatial regions which match the reference spectra, using red for hematite and green for the hexahydrate iron chloride. An additional contribution was identified as arising from carbon contamination due to the several measurements we had to perform to get a dataset with good statistics.