Reflectance spectra of X-complex asteroids selected as heterogeneous candidates in this study. Visible spectrophotometric and spectroscopic data were taken from Zellner et al. (1985), Bus & Binzel (2002), Sergeyev et al. (2022), and Gaia Collaboration et al. (2023). Data of Sergeyev & Carry (2021) were also used in the case of few visible spectral data. The green and yellow error bars represent the observational uncertainty of Marsset et al. (2020b). They are shown for the two most extreme spectra (Section 5). Different colors are used only for better readability. The black arrows show the slope uncertainty centered at the reflectance value of the spectra at 2.40 μm, as marked by the black dashed lines.