Study On The Minerals Composition And Structural Characteristics Of Weathering Curst Of Primary Nephrite In Russia

Nephrite from Russia often have varying thickness of the white weathering curst.Its transparency and luster is different from unaltered areas.On the basis of previous studies,the mineral composition,structural characteristics and spectral characteristics of the weathering curst of were studied by basic gemological property testing,EPMA,X-ray powder diffraction,infrared spectroscopy,laser Raman spectroscopy,specific surface meter,scanning electron microscope and other modern testing techniques.The weathering curst of the Russian primary nephrite is thick,white,yellow-white,earthy luster,opaque,with black and yellow impregnation in it.The relative density of the weathering curst is 2.747².869,and the microhardness is5.39⁵.96,both of which are obviously lower than the standard data of nephrite,which is related to its loose internal structure.EPMA and X-ray powder diffraction analysis showed that the main mineral in the weathering curst is tremolite without clay mineral and other phases.The content of K in the weathering curst was higher than that in unaltered areas and no obvious rule is observed for other elements,indicating that weathering does not change its chemical composition significantly.There is no significant difference in X-ray powder diffraction peaks between the weathering curst and the unaltered areas,indicating that weathering did not reduce the crystallinity of tremolite.Through the observation of scanning electron microscope and polarizing microscope,it is found that the crystal of tremolite in the regolith is in the shape of fine needle,with disorderly arrangement and large intergranular space.These structural changes cause the light to be reflected and refracted many times,resulting in a pure white,opaque,earthy appearance.The pore structure of the weathering curst was studied by using the specific surface meter.The specific surface area of the regolith was 15.432m²/g,and the pore volume was 0.060cm³/g,which was much larger than the specific surface area?1.960m²/g?and pore volume?0.003cm³/g?of unaltered areas.The pore size distribution diagram and adsorption-desorption curve of the regolith show that mesoporous and microporous structures exist in the weathering curst.The relative strength of the characteristic absorption peaks of 224cm^-1 and674cm^-1 in the Raman spectra of the the weathering curst is lower than the unaltered areas,indicating that the structure of the weathering curst is looser than unaltered areas.There are black and brown dendritic disseminated materials in Russian nephrite materials,which are very similar to nephrite gravel.The morphology and the main components were consistent with the black dendritic in nephrite gravel by EPMA and scanning electron microscope.Therefore,this feature should be carefully used as a sufficient condition for the identification of nephrite gravel.