Study On Mineralogical Characteristics And Genesis Of Green Nephrite From Xinjiang Uyghur Autonomous Region

In the domestic jade market, there are many different kinds of green nephritefrom different regions, and Hetian nephrite is of high-quality. Samples were collectedfrom Hetian-Yutian County, Xinjiang Uyghur Autonomous Region, its gemologicaland mineralogical characteristics, H, O isotopic features and the forming mechanismwere studied in this investigation.Observation under microscope shows that the main microstructure of this greennephrite is woven felt-like cryptocrystalline blastic texture, the arrangements of themineral particles result in its delicate texture and high toughness. SEM characteristicsillustrate its clean topography and compactness.Study on mineral composition indicates that the major mineral component istremolite, and then it turns into actinolite with the help of the increase of iron oxide.X-ray powder diffraction shows that the nephrite mainly consists of tremolite withminor chromite, chlorite, serpentine, clinopyroxene and apatite. The results of infraredspectroscopy and Raman spectroscopy coincide with the results of XRD. DTA curvedemonstrates that the structure of the tremolite was destroyed at900～1100℃. TGcurve demonstrates that the tremolite has such little water that its loss of weihgt wasonly0.89～1.33％when heated to900～1100℃.The geological origin of green Hetian nephrite is alteration of ultrabasic rock,and the internal black spot-like mineral is chromite which is a sign of ultrabasic rock.The analysis of hydrogen and oxygen isotopic compositions indicates that thehydrothermal fluids of Gobi aggregates are primary magmatic water, but thehydrothermal fluids of primary nephrite and gravel are unknow and still need moreinvestigation.It is important to evaluate the quality of green Hetian nephrite. According to acomparative study of the basic characteristics of Manasi nephrite, Russian nephriteand Canadian nephrite, Hetian nephrite is a variety of better quality and less crack.The color of Hetian nephrite is emerald green and the texture is delicate.