The Study On Gemmological And Mineralogical Characteristic Of Pink Dushan Jade From Nanyang

In the standard of Naming and Classification of Dushan Jade?GB/T 31432-2015?,the pink Dushan jade from Nanyang is called Hongdu jade,which is generally in the colors of hibiscus red,pink,light pink,peachy pink,etc.It often coexists with the green Dushan jade and the white one.In order to research the ordinary gemmological features,chemical composition,mineral composition and structure,spectroscopy characteristics,color genesis and color evaluation of the pink Dushan jade from Nanyang,many methods are used,such as the methods of microscope optical observation,X-ray fluorescence?XRF?,Electron microprobe analysis?EMPA?,Infrared spectroscopy?IR?,Raman spectroscopy,Ultraviolet-visible absorption spectra and CIE1976L^*a^*b^*uniform color.The results indicate that the pink Dushan jade in Nanyang is mainly composed of fine-grained crystalloblastic texture and massive structure.The refractive index is between 1.56 and 1.70,and"two refractive indexes"often appear at the same point.Mohs hardness is between 6.27 and 6.42.The relative density is between 3.00 and3.09.The chemical composition of pink Dushan jade from Nanyang is SiO₂,Al₂O₃ and CaO.It also contains Fe₂O₃,K₂O,Mn₂O₃,TiO₂ and Cr₂O₃.The mineral composition includes zoisite,anorthite,clinozoisite,epidote,calcite and hematite.The mineral texture includes porphyroblastic texture,metasomatic relict texture and fracture texture,which indicate that it has undergone hydrothermal and dynamic metamorphism in the mineralization process.The results of IR indicate that the content of zoisite in the pink Dushan jade is more than that of anorthite.Different mineral species and some mineral subspecies in the pink Dushan jade can be distinguished by Raman spectroscopy.The Ultraviolet-visible absorption spectra indicates that the 520 nm absorption band in the pink Dushan jade is probably related to the ⁵T₂?⁵E?D?crystal field transition of Mn³⁺,which is the main reason why Dushan Jade appears pink.According to the results of XRF and EMPA,it is suggested that the chromogenic minerals of the pink Dushan jade from Nanyang may be the zoisite and clinozoisite.Based on the CIE1976L^*a^*b^*uniform color space theory,the lightness of the pink Dushan jade L^*?[77.40,85.41],chroma C^*?[0.448,6.353],hue angle h^°_ab?[-3,33].The results of color difference calculation are basically consistent with the visual perception.