Figure 4

(a) Correlation between regression coefficients in the exponential function of geochemical effect for chondrite–lanthanides and Yb/La, and (b) the correlation between the coefficient of independent variable X (i.e., the coefficient of the radius of trivalent ion for lanthanides) and Yb/La in the C2 coal seam. The original data of REE refer to Table 1 (Dai Shifeng, 200710), the regression coefficients refer to Table 2.