Study On The Spectroscopy Characteristics Of “Taishan Biyu” And The Influencing Factors Of Color And Transparency

This paper presents the gemological,structural,compositional and spectral characteristics of Taishan Bi Yu by means of SEM,EDXRF,EPMA,FTIR,Laser Raman,and UV-VIS spectrophotometer,characterizes the color and transparency quantitatively,and discusses the influence factors of their color and transparency.Taishan Bi Yu is dark green under the reflected light,and rich in hues under the transmitted light,varying from light yellow green to dark green.It shows waxy to greasy luster and is slightly transparent or transparent with refractive index ranging from 1.562 to 1.565.The specific gravity of the Taishan Bi Yu is higher than 2.60.The inclusions are mainly magnetite,hematite and ilmenite.Chemical composition analysis shows that Taishan Bi Yu is composed mainly of Si O₂ and Mg O;other contents include Fe O,Al₂O₃,and Ni O.The isomorphic substitution of Fe^2+/3+instead of Mg²⁺is common in Taishan Bi Yu,which makes Mg O content lower than the standard value.The IR and Raman spectra characteristic absorption peaks of Taishan Bi Yu are consistent with those of antigorite,indicating that Taishan Bi Yu consists mainly of antigorite.Fe is the main chromogenic element of Taishan Bi Yu,whose characteristic absorption spectrum and color are mainly caused by the crystal field transition of Fe³⁺and the charge transfer from Fe²⁺to Fe³⁺.The transmittance of Taishan Bi Yu was quantified by UV-VIS spectrophotometer.Combined with the naked eye observation and unit transmittance t value,Taishan Bi Yu can be classified into four transparency categories:transparent,translucent,slightly transparent and opaque.The transparency of Taishan Bi Yu is mainly determined by the size,relative size and orientation of antigorite minerals.The main structure of"Taishan Biyu"is metamorphic structure.Samples having lepidoblastic texture show better transparency then leaf-like metamorphic texture,and the transparency of the equigranular texture sample is better than that of the inequigranular texture.In addition,the combination degree of mineral particles and fractures are also important factors affecting the transparency of Taishan Bi Yu.The color quantitative characterization of Taishan Bi Yu was conducted via the establishment of non-contact color measurement system.The results indicate that the samples have large range span in lightness,and belong to low to medium chromaticity with hue ranges between yellow green to green.The color of Taishan Bi Yu is related to its transparency and Fe content.Transparency mainly affects the lightness and chromaticity.The higher the transparency is,the higher the lightness and chromaticity are.The hue of the Bi Yu is mainly controlled by Fe content.With the increase of Fe content,the yellow tone decreases while the green tone increases.