Mineralogical Characteristics And Spectral Characterization Of Turquoise From Ma'anshan,Anhui Province

Ma'anshan is an important turquoise producing area in Anhui.In order to enrich the characteristics of the origin of turquoise,on the basis of field investigation and sample collection,the mineral composition,structure,chemical composition and spectral characteristics of turquoise have been systematically studied by Gemstone microscopy,Vickers hardness tester,Polarizing microscope,Scanning electron microscopy,X-ray powder diffraction,X-ray fluorescence spectrometer,Electron probe,Infrared spectrometer,Ultraviolet-visible spectrophotometer and micro-Raman spectrometer.The sample has a cryptocrystalline structure and a hull-like structure under the microscope.It is mainly associated with quartz,and there are also iron-like infiltrates distributed in veins.Quartz,Pyrite and Hematite appear in the surrounding rock near turquoise.Under the scanning electron microscope,they are irregularly massive,scaly,plate-like and long columnar structures.The loose turquoise's pores are obvious,the crystallites are arranged in disorder,and the dense turquoise's pores are less,the crystallites are arranged closely.The gradual decrease of the Fe_T/Cu ratio in the turquoise composition can stably indicate the transition of its color from green to light green and to light blue and to blue.The electron probe datas indicate the content of Al₂O₃,P₂O₅ and CuO is 36.56³9.94%,37.15³9.95%and 7.44⁹.24%respectively.The results of infrared spectroscopy and Raman spectroscopy analysis show that the spectral characteristics of natural turquoise are caused by the vibration of?OH?,?H2O?,?PO4?.Blue turquoise has stronger peak strength and larger peak area than green turquoise at?OH?stretching vibration peak.The absorption of ultraviolet-visible spectra is mainly located at 430,665 and 730nm.With the change of color,the absorption intensity of 730nm caused by Cu²⁺and 430nm caused by Fe³⁺shift from one to another,and the absorption broadband in 650⁶80 nm range will shift.Considered thoroughly by the XRF,EPMA data and spectroscopic characteristics,the occurrence of water in turquoise,binding mode and the content of Cu and FeT ions have a common impact on its color,indicating that the spectral characteristics of turquoise have a characterization significance for its color.