Study On Gemmological And Mineralogical Characteristics And Color-causing Mechanism Of Guizhou Jade From Qinglong,Guizhou Province

Guizhou Jade is a kind of quartz jade produced in the antimony deposit of Dachang Town,Qinglong County,Buyi and Miao Autonomous Prefecture,Southwest of Guizhou Province.The characteristic color is greenish blue to bluish green,rare red,yellow and other colors.In this paper,in order to explore the gemmological and mineralogical characteristics of the typical Guizhou Jade,then systematically study and analyze the structural characteristics and color-causing mechanism,the samples were studied by polarizing microscope,X-ray diffraction?XRD?,infrared spectroscopy,Raman spectroscopy,cathodoluminescence,scanning electron microscope?SEM?and X-ray energy dispersive?EDS?,X-ray fluorescence spectroscopy?XRF?,electron probe,whole rock analysis of trace elements,optical fiber spectrum and ultraviolet-visible spectroscopy?UV-VIS?.The main mineral composition of Guizhou Jade is quartz and dickite,while the minor mineral composition is fluorite,calcite,stibnite,pyrite,anatase,etc.The cracks and pores are mostly developed,and clay minerals are often enriched in the cracks and pores.The quartz content accounts for about 70⁸0%,and the dickite accounts for about 20³0%.Under the polarizing microscope,the quartz mostly presents hypidiomorphic-allotriomorphic granular forms,and the dickite presents fine scaly and page shape,embedded in the quartz crystal gap and cemented with quartz.In the high frequency region of the Raman spectroscopy from 3600³750cm^-1,the dickite shows three stepped sharp bands,which are Raman spectra of typical dickite,so as to distinguish the kaolinite group minerals.The main chemical component of Guizhou Jade is SiO₂ and Al₂O₃,and there are other trace elements such as K,Ca,S,Fe,V,Cr,Ti,Mn,which are related to the hydrothermal components in the metallogenic environment.There are often a small number of elements such as Cr,Fe,V,Ti in the form of isomorphism to replace Al in the dickite,and the substitution of Al for Si.In cathodoluminescence,the quartz emits little fluorescence,while the dickite emits blue-purple fluorescence due to internal crystal structure defects.The quartz vein interspersed in the interior of Guizhou Jade shows strong gray-yellow fluorescence with obvious zonary structure,and the quartz secondary enlarged edge shows gray-yellow fluorescence,zonary structure,which is the product of multiple growth and precipitation.Most of Guizhou Jade is dense massive structure,mainly granular structure,idiomorphic structure,radial structure and porphyritic structure.Under SEM,it is observed that Guizhou Jade is granoblastic texture and the dickite is distributed in the quartz grains or is wrapped in the quartz.Most of the quartz has a semi-angular contour and rich surface features.The crystal shape of dickite is mostly pseudo-hexagonal flaky or plate-like,with a high degree of idiomorphism.Generally,they are stacked and arranged in laminated,organ-like,page-like and vermicular aggregates,and the curved shape of the crystal can be seen.Through colorimetric analysis,the typical color of Guizhou Jade is greenish blue,low chroma,medium brightness.The cause of greenish blue is related to dickite,caused by Cr³⁺in the dickite,and the content of Cr³⁺directly affects the color depth of greenish blue.The red and yellow are related to the iron minerals attached to the mineral grains of Guizhou Jade,and the Fe element is directly related to the cause of the color,and the iron content of Guizhou Jade in red is higher than that Guizhou Jade in yellow.