Study on the Characteristics of Gemology and Mineralogy of “Xi'an Green” Jade

“Xi'an green” jade is produced in the south Qinling mountains of Shaanxi province. It is a high-quality green seal and jade carving material appearing in the jewelry market in recent years, and has been recognized by the market for its gorgeous color, delicate and moist. In this study, conventional gemological instruments, polarizing electron microscope, X-ray powder diffractometer, electron probe and scanning electron microscope were used to systematically study the gem mineralogy of jade and surrounding rock, including the relationship between jade and surrounding rock, composition characteristics, structural characteristics, color genesis and other aspects. The conclusions are as follows:① The occurrence of jade is in the form of mass and vein. The surrounding rock is mainly marble with a small amount of flint, which is caused by alteration metasomatism and mineralization. Quartz veins are commonly symbiosis with them in the later period, and the relationship is interspersed and metasomatism.② Jade is mainly composed of illite, containing a small amount of chromica, vanadium mica, apatite, limonite, etc. ③ The jade structure is characterized by the close arrangement and accumulation of illite flake minerals, The particle size of fine jade is about 0.002×0.004mm~0.007×0.009mm, and the particle size of coarse jade is 0.006×0.006mm~0.025×0.025mm.and the shape and size of the minerals affect the color and delicacy of the jade. ④ The cause of the green color of jade is related to the V element in illite. the content of V element is positively correlated with the depth of green, and the Ni element may also contribute to the origin of color. The yellow-brown and red-brown bands are mainly caused by iron-containing metallic mineral. In addition, preliminary suggestions for quality evaluation are made, including color, structure, impurity, lumpiness and process, which can provide some theoretical basis for the market.