Study On Gem Mineralogy And Structure Characteristics Of Pteridophyte Silicified Jade From Heilongjiang

According to GB/T 34098-2017,quartzite jade with the metasomatic pseudomorph of silica is collectively referred to as‘silicified jade'.The silicified jade from Heilongjiang studied in this article is a fossil formed by the ancient tree fern replaced by silica,which retains the structure of the plant.Because of its special pattern,it has attracted the attention of collectors.As an emerging jade,the pteridophyte silicified jade from Heilongjiang lacks systematic research on gemology and mineralogy,and there is no systematic standard for its quality evaluation on the market.Therefore,this article study and analyze the general gemological characteristics,structural characteristics,mineral composition,chemical composition and formation environment of pteridophyte silicified jade from Heilongjiang with general gemological testing,polarized microscope,field emission scanning electron microscope,X-ray powder diffractometer,Fourier infrared spectrometer(FTIR),Raman spectrometer(Raman),Difference Thermal analysis,X-ray energy dispersive spectrometer,X-ray fluorescence spectrometer,inductively coupled plasma mass spectrometer,isotope ratio mass spectrometer and so on.Studies have shown that the gemological properties of silicified jade from Heilongjiang are similar to common quartzite jade.Jade can be seen with thick tube,thin tube and filamentous plant structure which is composed of plant stems,roots,leaf traces,etc.The stems are tubular with larger diameter,mainly composed of pith,vascular bundles(including xylem and phloem),cortex and other structures.Roots are small in diameter,point-like,filamentous,and composed of a central pillar and cortex opposite to the leaf trace.The mineral composition of pteridophyte silicified jade from Heilongjiang is?-quartz,and it also contains a small amount of plagioclase,hematite,dolomite,barite,water and organic matter,but the content of organic matter and water is not high,so quartz replacement is relatively complete.The mineral particles are mainly fine-coarse quartz particles and fibrous chalcedony.Among them,small other-shaped quartz particles account for the majority,while semi-automorphic quartz,automorphic quartz and chalcedony account for less,and the crystallinity is poor.Quartz particles change from outside to wall to inside of the plant structure pores,showing a change pattern from other-shaped,fibrous,short columnar,and coarse granular.Therefore,in the process of quartz replacement,it should replace the inside of the tube holes and pores,firstly,and then replace the outwards.The main chemical component of pteridophyte silicified jade from Heilongjiang is Si O₂,and it also contains traces of Fe₂O₃,Mg O,Al₂O_3,CaO,K₂O,Mn O,Ti O₂,P₂O₅,and other elements.The content of rare earth elements is relatively low compared to the content of the continental crust.There is a large differentiation between light and heavy rare earth elements content,light rare earth elements are relatively enriched.The anomalies of?Ce are not obvious,and the value of?Eu shows negative anomalies.The characteristics of major and trace elements and the composition of silicon and oxygen isotopes indicate that the silicified jade belongs to hydrothermal origin.The formation environment was freshwater,and the hydrothermal temperature was relatively high,about 70?.