Fig. 8. Spectral signatures of the composition thickness maps of the exterior area shown in Fig. 6, with both (a, b and c) uncorrected PS-Io and (d, e and f) CM-Io corrected spectra. Spectra (a) and (d) refer to mineral and pore space signatures, respectively. Spectra (b), (c), (e), and (f) show elevated optical density as a result of absorbance by mineral matter. Residual errors for the fitted spectra (d), (e), and (f) are shown with their root variance, .