Formation Mechanism and Color Genesis of the Yiyuan Jade in Luanchuan, Eastern Qinling (Central China): Implications for the Provenance Tracing of Ancient Jade Artifacts

The Yiyuan jade from Luanchuan County, Henan Province (Central China), has been known since the Neolithic period and provides a scientific reference for tracing the provenance of jade artifacts from nearby Neolithic sites. In this study, the mineralogical characteristics and color genesis of the Yiyuan jade were investigated using petrography, XRD, SEM–EDS, FTIR, UV–Vis–NIR, and EPR spectroscopy. The jade occurs in four color varieties and is petrologically classified as serpentine–bearing dolomitic marble formed by Neoproterozoic gabbroic magma intrusion and subsequent low–temperature alteration. The color variations correspond to distinct mineral assemblages. White jade is dominated by calcite and dolomite; bluish–black jade by antigorite, clinochlore, and chamosite; bluish–white jade contains intermediate proportions of these phases; and green jade consists mainly of epidote and actinolite. The bluish color intensity shows a quantitative correlation with the green mineral content. Bluish–white appears when antigorite and clinochlore together account for 5%–40%, bluish–black when they exceed 40%, and bluish–gray when chamosite exceeds 10%. The bluish–black coloration is controlled by the dense fibrous interwoven microstructure of antigorite rather than by Fe or other elemental chromophores. These distinctive features serve as diagnostic criteria for identifying bluish–black jade materials from Neolithic sites in the Luanchuan region.