The spectral slope of R₁₅₅₀/R₇₅₀ versus R₇₅₀. (a) R₇₅₀ versus R₁₅₅₀/R₇₅₀ of all data. Furthermore, the spectra of the returned Apollo lunar samples were sourced from the LSCC database, and the maturity data for the LSCC samples were obtained from L. A. Taylor et al. (2010). (b) R₇₅₀ versus R₁₅₅₀/R₇₅₀ of M³ from (a). The black arrow indicates the direction of increasing maturity, while the gray dashed line represents the spectral alterations trendline fitted using a sixth-order polynomial.