Gemological And Mineralogical Study On The Black Skin Nephrite Gravel

The market demand for Nephrite Gravel material is constantly rising,and its value is also rising.However,the consumer market is flooded with a large number of imitation products,which affects the normal market order.The identification of the sub-material mainly depends on the identification of the sub-material skin color.Therefore,the color-causing factors of nephrite skin color have always aroused wide attention of scholars.Black skin is a common skin color of nephrite sub-materials and has a high market share.In this paper,the cyan and black sub-materials in Hotan area are used as the research object.Microscopic observation,environmental scanning electron microscopy(ESEM),and synchrotron radiation X-ray diffraction spectrum(SRXRD),micro-infrared spectroscopy,Raman spectrum,and X-ray photoelectron spectroscopy(XPS)test methods,the sample morphology,element distribution,skin color and meat quality of cyan and black sub-materials in Hotan The phase composition and the morphological distribution of C and Fe elements were detected and analyzed.Studies have shown that: In the sample matrix of nephrite,there are Si,Al,Mg,Ca,O elements and there are a wide range of homogenous substitutions,in which the proportion of Fe in the black and cyan regions is similar,about 1.4%,The iron content is relatively low,and the content that leads to the black color of nephrite is not reached.XPS detection results show that with the deepening of the color density,Total(Fe2+)/Total(Fe3+)in the brown vein area is significantly higher than that in the light-colored area;The black impregnation depth of this sample is a few centimeters,the thickness is deep,and there is no obvious difference between the black and cyan boundary lines in the BSE image.The element test shows that there is no Mn element,and the black in the nephrite and the sample matrix appear to be impregnated,with branches There are obvious differences in crystal morphology;Raman spectroscopy and scanning electron microscopy results show that there are solid solutions of rutile and sphene,and some dark graphitized substances are detected in the dark-enriched part,and as the color of the black veins deepens,The spectrum peak becomes more obvious,XPS test is performed in different black areas of the sample,the standard peak of carbon(284.6 e V)is attributed to the CC bond,its intensity becomes larger as the color of the detection area deepens,and the intensity at the deepest point It is 78.6% of the intensity at the shallowest point.The main conclusions are as follows.Its main mineral is tremolite,diopside,rutile,sphene,zircon,chlorite,and carbonaceous inclusions are secondary minerals.Tests show that the black skin color is due to:(1)carbonaceous materials impregnated into the cracks and appear dark;(2)a large amount of rutile sphene solid solution opaque minerals;(3)brown bands caused by Fe3+.This study can provide a basis for the cause of the color formation and origin identification of black nephrite in Xinjiang.