Mineralogical Characteristics and Color Genesis of Zibai Jade

Zibai Jade is a recently identified hydrogrossular-dominant jade originating from Shaanxi Province, China. It constitutes a polymineralic aggregate composed predominantly of hydrogrossular, with minor proportions of vesuvianite, diopside, chlorite, uvarovite, and calcite. A multi-method analytical approach was employed to characterize the jade, incorporating conventional gemological testing, polarizing microscopy, SEM, XRD, BSE, XRF, EPMA, as well as UV-Vis, infrared IR. These techniques enabled a detailed examination of its mineralogy, surface features, and color origin. The stone displays heterogeneous color distribution, featuring a base hue of light green to yellowish-green, accompanied by distinct occurrences of emerald-green spots, dark green spots, mossy green inclusions, white patches, white veinlets, and black dot with a green ring.Microanalytical results indicate that the emerald-green spots are principally composed of uvarovite. The dark green sports are dominated by hydrogrossular, diopside, and chlorite. Fibrous green inclusions consist mainly of chlorite and Cr-bearing grossular. White patches and veinlets are primarily composed of calcite. The black dot with a green ring are predominantly comprised of chromite and uvarovite.Coloration is attributed to the combined influence of Fe and Cr3+. The formation of the jade involved three mineralization stages: protolith accumulation, high-temperature metasomatism, and retrograde alteration. The interplay of these processes resulted in the development of Zibai Jade, which exhibits a dense texture and attractive coloration.