Investigation of the Coloration Mechanisms of Yellow-Green Nephrite from Ruoqiang (Xinjiang), China

This study systematically investigates the color origin and coloration mechanisms of yellow-green nephrite from Ruoqiang, Xinjiang, using multiple analytical techniques including hyperspectral colorimetry, X-ray fluorescence (XRF) spectroscopy, titrimetry, laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS), Raman spectroscopy and ultraviolet–visible (UV-Vis) spectroscopy. A pioneering quantitative model (R2 = 0.942) was established between hue (H) and the Fe2O3 ratio (Fe2O3/TFe), revealing that the coloration mechanism is jointly governed by Fe3+ charge transfer (300–400 nm absorption band) and Fe2+→Fe3+ transitions (600–630 nm absorption band). Furthermore, the intensity variation in the 3651 cm−1 Raman peak serves to further confirm the critical role of Fe3+ occupancy in the tremolite lattice for color modulation. In combination with the partition patterns of Rare Earth elements (REEs) (right-leaning LREE distribution with negative Eu anomaly) and trace element characteristics, this study supports the classification of Ruoqiang yellow-green nephrite as a high oxygen fugacity magnesian marble-type deposit. In this type of deposit, the ore-forming environment facilitates Fe3+ enrichment and yellow-green hue formation. The findings provide new theoretical insights into the chromatic genesis of yellow-green nephrite and hold significant implications for its identification, quality grading, and research on metallogenic mechanisms.