Fig. 9

(a) The distinguishing samples’ mineral composition logic. (b) The L* and w(Mn) of group 1 are negatively correlated; the L* and w(Fe) of group 2 are negatively correlated. (c) There is no obvious correlation between the chroma C* and w(Mn) of group 1, showing a positive correlation first and then a negative correlation; the chroma C* and w(Fe) of group 2 samples are positively correlated. (d) The hue angle h° and w(Ca) and w(Cu) of group 3 samples are all negatively correlated.