Continuum-removed infrared spectra of basaltic samples (BAS) at different grain sizes (<50, 50–200, 200–500 and 500–1000 µm) mixed in different proportions (from 1 to 50%) with synthetic amorphous carbon [SAC], spectra are limited in the range 7.5–15.5 µm to highlight the RB region, shown in panels A, B, C, and D. Panel E: band area, normalized at the value of pure BAS samples, evaluated for each series of mixing. Panels F, G, H and I: height of the peak of RBs normalized at the value of pure BAS and evaluated for each series of mixtures (see Table A.1 for the precise wavelength and method used for peak depth evaluation).