A Gemological Study Of Tremolite Jade In Yeniugou,Qinghai

Tremolite jade is a traditional Chinese jade with mild texture and rich cultural connotation,which is deeply loved by the Chinese people.At present,the research on Yeniugou tremolite jade mainly focuses on spectroscopy and mineral composition.The research results did not show the origin identification of tremolite jade in this mining area.In this paper,samples of Qinghai Yeniugou tremolite jade sample were tested for conventional gemological characteristics.The results showed that the color of samples is mainly green to green-white,purple to smoky blue or white.It can be seen that the brown color is impregnated,and the samples have vitreous luster to greasy luster,are translucent-subtranslucent,of poor lubricity;the refractive index is about 1.61（spot measurement）,relative density can reach 2.98,hardness is 6～6.5,and the fluorescence is inert.Combined with electron probe and X-ray powder crystal diffractometer test analysis,it is shown that the main mineral component of Qinghai Yeniugou tremolite jade is tremolite,and the minor minerals are diopside and calcite;XRD test results show that the crystallinity of Qinghai Yeniugou tremolite jade’s main crystal phase is significantly higher than that of Afghanistan and Tanghe,and the hand specimens show the characteristics of relatively coarse particles,and relatively high transparency.Under the polarized light microscope,its structure is felt-like interweaving structure,micro-fibril metamorphic structure,micro-radial metamorphic structure to broom-like structure.The infrared spectrum and Raman spectrum of tremolite jade from this area are basically consistent with the peaks of tremolite jade.The infrared characteristic spectrum is concentrated in the ranges of 400～1200 cm^-1 and 3400～4000 cm^-1,of which the absorption peak near 3672cm^-1 is the stretching vibration of OH group,which is related to the OH stretching vibration of two M1 positions and one M2 position in the tremolite structure;Raman spectrum peak positions are mainly concentrated in the range of 100～1100 cm^-1.Parts of both the Raman and infrared spectral peaks have different degrees of deviation,the former’s deviation range is 1～45 cm^-1,the latter’s deviation range is 1～4 cm^-1,combined with the chemical composition test results,it is inferred that those deviations are related to the trace elements in the sample.The results of ultraviolet-visible absorption spectra and trace elements test showed that the main color-causing ions of smoky purple tremolite jade are Fe³⁺and Mn²⁺,and the green and green-white colors are mainly related to Fe²⁺.LA-ICP-MS test results show that the trace elements of Qinghai Yeniugou tremolite jade are obvious negative anomalies of Eu,weak positive and negative anomalies of Ce,Th-Ce-Hf-Sm loss and U-La-Sr-Y enrichment;among them the U enrichment and Sm loss are very obvious,which is quite different from other origins,and can be used as the identification feature of origin of tremolite jade from this mining area.Combining the results of major elements,trace elements,rare earth elements,and spectral characteristics,it is believed that the formation of Qinghai Yeniugou tremolite jade is the result of the combined action of magnesian marble,diabase and hydrothermal fluid;shearing plays a vital role in the mineralization process of Qinghai Yeniugou tremolite jade.