Abstract:Nephrite, widely distributed in nature, is one of the earliest natural jade resources developed and utilized in human history. The relatively well-known nephrite deposits in China include Hetian of Xinjiang, Xiuyan of Liaoning, Golmud of Qinghai and Hualien of Taiwan as well as some nephrite deposits discovered since the 1990's such as Xiaomeiling in Liyang of Jiangsu and Mianyang of Sichuan. Previous studies of nephrite were almost confined to the nephrite from a single producing area and were lacking in comparative work. There is also a lack of systematic research on the causes responsible for the differences in the texture of nephrites from different producing areas, which results in shoddy phenomena in the current market. Therefore, it is particularly important to seek for identifying symbols and quality appraising factors for nephrites from different producing areas. In this paper, the authors employed polarizing microscope, LA-ICP-MS and SEM analysis to study typical varieties of Xinjiang and Xiuyan nephrites. Test results show that physical properties of the nephrites from the two producing areas are similar to each other, but Xiuyan nephrite is not so good as Xinjiang nephrite in luster, transparency, and polished finish. There is almost no yellow-white jade and green jade in Xinjiang nephrite, and the yellow jade common seen in Xinjiang nephrite is on the whole not observed in Xiuyan nephrite, which accounts for the significant difference in color between the nephrites from the two areas. The content of the common coloring elements such as Be, V, Cr, Co, Ni and Cu in the two nephrite producing areas is not consistent, and there exists no corresponding relationship between the changing trend and the varieties. The total content of trace elements is the highest in green nephrite, and such elements as Be, Ni and Cu have a certain impact on the green color of nephrite. The ΣREE values of Xinjiang nephrite range from 1.4698×10-6 to 4.2217×10-6, the values of (La/Yb)N vary from 0.5663 to 10.8392 and δCe from 0.8115 to 0.9866; the ΣREE values of Xiuyan nephrite range from 5.1850×10-6 to 20.4230×10-6, the values of δCe vary from 0.8386 to 0.9885, and (La/Yb)N from 2.1071 to 5.6884. The nephrites from the two producing areas generally have low rare earth elements and clear differentiation of LREE and HREE, suggesting the enrichment of HREE. In addition, δEu are characterized by both positive and negative anomalies. The REE partition curve shows the REE features of multi-sources of ore-forming fluids and multi-period mineralization. The difference in the ore-forming source and the environment is the basic factor causing the different REE compositions of the nephrites from the two nephrite producing areas. Photomicrographs show that Xinjiang nephrite is mainly composed of fibrous, columnar, needlelike and flaky tremolite, and its impure minerals are composed of occasional limonite, ferric oxide and chlorite, illite and other clay minerals, whose content does not exceed 1%. It is colorless under polarization microscope and assumes middlepositive relief, with the relief gradually increasing with the increase of Fe content in samples. Its interference color is yellow to purple in Grade I. Xiuyan nephrite is similar to Xinjiang nephrite in mineral composition and structure, but it has larger particle sizes, poor compactness and larger gaps between the particles. The tremolite mainly has radiate fibrous and columnar shape through SEM observation, which seems to be the common character of the nephrites from the two producing areas, but Xinjiang nephrite has the most typical feltlike fiber woven blastic texture, with the particle sizes generally less than 3 μm and the lengths of columnar and fibrous particles generally less than 10 μm. Xiuyan nephrite commonly has micro-fiber and micro-leaf-shaped structure, and the tremolite grains assume leaf-shaped and fibrous distribution. The tremolite grains are thicker than those of Xinjiang nephrite, and the lengths are mostly in the range of 10~20 μm, with rather bad density. In addition, there are often uneven fractures or faults developed in the cleavage direction of tremolite in Xiuyan nephrite, which affects the quality of nephrite to a certain extent and seems to be an important factor causing the fact that its quality is not so good as that of Xinjiang nephrite.