光谱学与光谱分析, 2021, 41(2): 643, 网络出版: 2021-04-08

蓝色蛇纹石玉的谱学特征

Spectroscopic Characteristics of Blue Serpentine
作者单位
摘要
近期在玉石市场上出现了一种名为“天青冻”的蓝色蛇纹石玉, 为蛇纹石玉的一个新品种。 采用偏光显微镜、 扫描电子显微镜、 激光剥蚀电感耦合等离子质谱仪和X射线粉晶衍射仪分析其结构特征、 化学和矿物组成, 并采用傅里叶变换红外光谱仪、 激光拉曼光谱仪和紫外-可见分光光度计对其谱学特征进行研究。 结果表明蛇纹石呈叶片状交织成毛毡状结构, 并含有菱面体状的杂质矿物白云石。 同时, X射线衍射谱2.53 ?(d202), 1.56 ?(d062)和1.54 ?(d060)的特征衍射峰以及红外吸收光谱中3 673, 997和641 cm-1的特征吸收峰表明其属叶蛇纹石, 1 098和1 086 cm-1的特征拉曼峰指示了白云石和方解石的存在, 这与其形成于SiO2热液交代白云岩的成矿环境相关。 化学分析表明蓝色蛇纹石玉中的Fe元素含量较其他常见蛇纹石玉低。 紫外可见吸收光谱中Fe2+→Fe3+电荷转移引起的强630 nm吸收带致其蓝色, Fe2+→Fe3+电荷转移引起的724 nm弱吸收带会导致其产生绿色调, 而由Fe2+和Fe3+自旋禁戒跃迁分别导致的537和488 nm弱吸收带对颜色影响较小。
Abstract
Recently, a new species of serpentine, which color is blue, named “Tian Qing Dong” appeared in jade market. Structure characteristics, chemical and mineral compositions have been investigated with a polarizing microscope, Scanning Electron Microscope, Laser Ablation Inductively Coupled Plasma Mass Spectrometry and X-ray powder diffraction spectrometer. Based on these measurements, spectroscopic characteristics are studied by using Fourier Transform Infrared Spectrometer, Raman spectrometer and Ultraviolet-Visible spectrometer. Results show that serpentine is scaly and interlocked into the felt structure. Besides, serpentine contains impurity mineral that is rhombohedron dolomite. Meanwhile, XRD results show characteristics diffraction peaks that are 2.53 ?(d202), 1.56 ?(d062), 1.54 ?(d060) and FTIR spectrum present characteristics absorb peaks which are 3 673, 997, 641 cm-1, they are confirmed that antigorite is the main mineral. There are 1 098 and 1 086 cm-1 of characteristics Raman shift exist which are belong to dolomite and calcite, these clues have indicated blue serpentine may be formed after the metasomatism which happened between dolomite and hydrothermal solution which contains SiO2. Chemical analysis shows that the concentration of Fe of blue serpentine is far lower than familiar species. UV-Vis results show that Fe2+→Fe3+ intervalence charge transfer (IVCT) transition generates a strong and broad absorption band which center is about 630 nm induce blue color, while Fe2+→Fe3+ IVCT transition also generate a weak absorption band which is 724 nm present green color. The spin-forbidden transition of Fe2+ and Fe3+ have generated 537 and 488 nm, and both are weak absorption that has not to contribute to present color.
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