Comparison of spectral trends described by Pieters (2018, see Fig. 2 therein). The magnetic separates in panel a are taken from RELAB database³, with Sample-IDs LS-JBA-180-M, LS-JBA-180-N and LS-JBA-180-P for magnetic, non-magnetic and bulk samples, respectively. These laboratory spectra were originally acquired by Adams & McCord (1973) and reproduced in Fig. 2B of Pieters (2018). The CSSI for the spectra of magnetic vs. non-magnetic material corresponds to 0.044. The bright swirl, dark lane and fresh crater spectra were derived from M³ data by Pieters (2018), we extracted the spectra shown in panel c manually from Fig. 2A of Pieters (2018). The CSSI value for the spectral pair of bright swirl and dark lane corresponds to 0.108.