Comparative Study on Mineral Components,Microstructures and Appearance Characteristics of Nephrite from Different Origins

Nephrite is mainly sold on the market in China(Xinjiang,Qinghai Province and Liaoning Province),Russia,Canada,South Korea and other places at present.The main kinds of jade are white jade,grayish jade,gray jade and green jade.Jade from different origins show the similar characteristics in mineralogy and petrology.However,it shows subtle differences in nephrite appearance from different origins due to the differences in mineral assemblages and tremolite crystallinity,particle size and arrangement.This study is aiming to find the common and different characteristics of nephrite from various orgins and to provide a more detailed theoretical guidance for identification. Using polarizing microscope, X-ray powder diffraction, scanning electron microscopy (SEM) and ICP-MS,the chemical compositions, mineral assemblage, microstructures and appearance characteristics of the main varieties of nephrite are studied. The results show that the chemical compositions and main minerals of nephrite from different origins are similar. However, there are differences in trace elements and secondary minerals, which could be a certain significance for identification. In general, white jade and grayish jade from Xinjiang, high quality white jade from Qinghai Province and Russia are flet-like cryptocrystalline blastic texture with high content of tremolite, where fiber structure is small and closely intertwined. Therefore, the jade is fine, glossy in appearance. While gray jade from Xinjiang, part of white jade, grayish jade from Qinghai Province, white jade from Xiuyan and South Korea are micro-fibrous interlocking texture, microfibre flaky blastic texture, microfibre granular crystal-loblastic texture and porphyroblastic texture. Content of tremolite in jade from those areas is relatively low, and fibers are coarse with large gap, which lead to rough texture and poor gloss in appearance and toughness decreasing. The structural types and crystallinity of jasper from Xinjiang,Russia and Canada are similar and it shows little difference in appearance characteristics.