Comparative Analysis of Gemmological Characteristics of Brown-white Nephrites from Xinjiang,Qinghai and Russia

In order to identify the differences of structures，mineral components and genesis among the brown－white nephrites from Xinjiang，Qinghai in China and Russia，on the basis of appearance characteristics observation，this paper investigates the brown－white nephrite samples from Xinjiang，Qinghai in China and Russia by means of conventional gemmological methods，polarizing microscope，XRD and EPMA，and carries out a comparative analysis of structures，mineral components，chemical compositions and formation reasons.The results show that the main mineral component of the brown－white nephrite samples is tremolite while the secondary mineral component is different.The brown－white nephrite samples from Xinjiang in China and Russia have felt－like interweaving texture while the brown－white nephrite samples from Qinghai in China has fibrous blastic and fibrous cryptocrystalline texture.Brown is the secondary colour，which is caused by limonite.According to the related geological background and weathering features，it can be inferred that the different appearance characteristics of the brown－white nephrite from three localities are mainly influenced by the surrounding environment changes after the later stage and finishing stage of metallogenic period of nephrite.