Color,Structure And Identification Features Of Beihong Agate

"Beihong agate"is a kind of cryptocrystalline quartz jade mainly produced in Xing'an Mountains regions of Heilongjiang province."Beihong agate"usually shows a red appearance with yellow tone.In this paper,the gemological mineralogical characteristics of"Beihong agate"with different colours and special structures were studied by microscopic magnification,XRD,Raman spectroscopy,infrared spectroscopy,optical fiber spectrometer,UV-VIS spectroscopy,?-XRF Mapping,chemical analysis of rock elements,ICP-MS and SEM-EDS.Based on these results with previous studies,an identification method for distinguishing"Beihong agate"from"Nanhong agate"was put forward.The main mineral composition of"Beihong agate"is?-quartz,while the minor mineral composition is moganite,goethite and trace amounts of hematite.Goethite and hematite show a disseminated and banded distribution pattern.The content and existing form of Fe element can affect the tone of"Beihong agate"in varying degrees.The minimal value in the range of 400-700 nm in 1st derivative spectrum of UV-VIS spectrum can be used in practical identification.The chroma of the"Beihong agate"is generally lower than"Nanhong agate",but its size and transparency are higher than those of"Nanhong agate".In Raman spectra,the characteristic peak area ratio of moganite to?-quartz(A₅₀₁/A₄₆₃)of"Beihong agate"is stable at 0.15-0.36,while that of Nanhong agate from Sichuan and Yunnan is stable at0.00-0.08 and Nanhong agate from Gansu is stable at 0.00-0.11.Further testing of different kinds of quartz Jade A₅₀₁/A₄₆₃ in the later period can be used to provide basis for the regional distribution of quartz Jade.The quartz in"Beihong Agate"mainly exhibits three structural types:fine-grained,fibrous and idiomorphic structure.Usually,it has crystallization order from fine-grained structure to fibrous structure to idiomorphic structure,of which idiomorphic structure can be absent.The crystallization order reflects the gradual increasing crystallinity of hydrothermal fluids forming agate.On the basis of these three basic structures,extremely fine grain structure,fine grain-fibre structure and louver structure have been found.It is presumed that the content of Fe in the hydrothermal fluids is high,and the iron minerals are distributed in different bands of"Beihong agate"as a whole in a mode of oscillation,and their distribution is related to the silicon dioxide in the crystallization process of agate.The structural transformation to high order degree has restraint effect.The moganite in the"Beihong agate"is mainly distributed in fine-grained and fibrous textures,and almost doesn't exist in idiomorphic quartz.The content of moganite and?-quartz indicates a process of oscillation during the process of crystallization of agate from fibrous structure to idiomorphic structure.The distribution of K,Ti,Cr,Mn and Zn in idiomorphic quartz is obviously exclusive.The differentiation of these elements may also affect the growth of different structural types of"Beihong agate".