Time evolution of spectral parameters of (a) olivine and (b) pyroxene. Each curve corresponds to one type of irradiation and connects points denoting individual irradiation steps. H⁺ stands for hydrogen, He⁺ for helium, and Ar⁺ for argon ions. Time, t, was estimated for 1 au (see Appendix C for more detail), A_λ denotes albedo at a given wavelength, s stands for the spectral slope, and BS_λ stands for the strength of a band centred at a given wavelength λ. All parameters are divided by the corresponding spectral parameter of the fresh (f) material and include error bars. For details of pyroxene spectral slope changes, see Fig. 4.