Reflectance spectra of the minerals used in the modelling procedure as calculated from the Mie-Hapke radiative transfer code. Spectra are normalised to unity at 0.75 μm and offset by 0.2 unity with respect to one another for visibility. To highlight the spectral features of each specie and their relative intensities, we removed the continuum by dividing each spectrum by a line that fits the spectrum at 0.75 μm and 2.40 μm. The red curves correspond to a distribution of grains with large sizes compared to the wavelength (20−30 μm), whereas the black curves correspond to a distribution of grains smaller than or similar to the wavelength (0.1−2.0 μm). Since no optical constants were available for pyrrhotite, we used a reflectance spectrum from the USGS database for this mineral. See Sect. 4.2 for a discussion of the reflectance spectrum of amorphous olivine.