Fig. 4. Cluster pixel plots of components 2 and 3 show spectral characteristics of mineral and organic matter, color-coded for each cluster (color legend on top axis). Yellow color represents mineral cluster pixels separated from cluster pixels of organic and organomineral complexes by the blue (a) and green (b) clusters of pore space pixels. Pixel separation with an optical density gradient (axis component 2), distinguishes C chemical species in the organic or organomineral matter, and is noticeable only in (a) but not (b) on the axis component 3.