Study On Microstructure And Mineralogy Characteristics Of Petrified Wood From Xinjiang And Myanmar,and Discussion On Its Genesis

Petrified wood is one kind of quartziferous jade varieties,which is made up of silicon dioxide in the way of replacing the organic parts of the ancient buried trees in the geological conditions of hydrothermal activity.Petrified wood can be found in lots of places around the world and is drawing more and more attentions from experts of all circles.Most of the Petrified woods in the Chinese jewelry market are mainly from Myanmar and Xinjiang,whose time,backgrounds and wood species have obvious differences.In this paper,polarizing microscope and scanning electron microscope(SEM)were carried out to analyze the microstructures and mineralogical characteristics of petrified wood from Qitai,Xinjiang;X ray powder diffraction(XRD),infrared spectroscopy(IR)and Raman spectroscopy methods were used to analyze the mineral compositions,and X-ray fluorescence spectroscopy(XRF),electron microprobe analyses(EMPA)were carried out to obtain the chemical composition data.Through rock-mineral identification and analysis of the whole rock,the surrounding rock of Qitai petrified wood in Xinjiang was tested and analyzed.With isotope analysis on oxygen,carbon isotopes of Myanmar and Xinjiang petrified wood,and all the data and analysis have got above,the paper synthetically analyzed and discussed the characteristics of petrified woods from Myanmar and Xinjiang from microstructure and mineralogical aspects.The samples from Xinjiang and Myanmar are white,brown,and dark brown,and the gemological features such as refractive index,proportion and hardness are similar to that of aphanocrystalline quartz.Petrified wood from Xinjiang mainly consist of Si O₂,and also contains a certain amount of water and organic matter,as well as siderite and burnt ochre;its crystallinity is poor,generally the higher one can reach4.456 and the lower one at 1.538.Petrified wood from Xinjiang presents the microstructure of the soft wood such as axial tracheids,pits,axial parenchyma,rings,wood rays,resin canal.On the other hand,Petrified wood from Myanmar presents the microstructure of the hard wood such as ducts and pores.The main minerals grow In the plant structure are quartz,chalcedony and opal,and they have the grain size of nano-scale to micron-scale and the shape of pectinate,granulous and radial patterns.Growth hillock,twins,and conchoidal fracture can be found on crystal plane.The surrounding rock is tuffaceous sandstone,and its main composition is clay,and it has gone through ferritization.It is inferred that the petrified wood from Xinjiang has been formed at the temperature of 10?40?,and has gone through many times of metasomatism and deposition.Xinjiang Qitai petrified wood is formed in a low-high temperature hydrothermal fluid containing certain siliceous materials.The age of formation is speculated to be Jurassic in the Mesozoic era.The volcanic activity caused the trees to be buried,and metasomatism and recrystallization repeatedly took place in an oxygen-deficient environment and some deposition and metamorphism occurred at the later stage.