巴西Minas Gerais彩色电气石的宝石矿物学特征

Gemmological and Mineralogical Characteristics of Coloured Tourmaline from Minas Gerais State,Brazil

利用电子探针、X射线光电子能谱仪、紫外-可见光光度计和傅里叶变换红外光谱仪对产自巴西MinasGerais地区、不同颜色的彩色电气石样品进行了宝石矿物学特征研究。电子探针测试结果显示，该电气石样品中Al2O3和Na2O的质量分数较高，FeO的质量分数相对较低，且含有一定量的MnO和Cr2O3;X射线光电子能谱分析初步证实该样品为锂电气石；结合化学成分与紫外-可见光透过光谱的分析结果认为，微量元素Fe^2＋，Fe^3＋，Mn^3＋，Ti^4＋和Cr^2＋是巴西Minas Gerais彩色电气石样品致色的主要因素之一；红外吸收光谱测试结果显示，该样品在1200～1450cm。范围内存在强的B-O基团致伸缩振动带，含有BO3原子团；其在3000-3750cm。范围内具有H2O和羟基离子致双峰伸缩谱带。比较不同颜色电气石样品的红外吸收光谱发现，其光谱频带数及位置与电气石中的类质同象和化学成分有关。

The gemmological and mineralogical characteristics of the different coloured tourmaline samples from Minas Gerais State,Brazil, are studied by using the electron microprobe （EMPA）, X-ray photoelectron spectrometer （ XPS）, ultraviolet-visible spectrophotometry （UV-VIS） and Fourier transform infrared （FTIR） spectroscope. The results show that the contents of Al2O3 and Na2O are relatively higher and the content of FeO is relatively lower, with a certain amount of MnO and Cr2O3 in the samples by EMPA, which are primarily approved as Li-tourmaline by XPS. Based on the analysis of chemical compositions and UV-VIS transmission spectra,the one of the colouring factors of the samples is related to the trace elements such as Fe^2＋ , Fe^3＋ , Mn^3＋ , Ti^4＋ and Cr^3＋. The IR absorption spectrum results show that the strong stretching vibration band at 1 200-1 450 cm^-1 is induced by B-O group for proving BO3radical and the double stretching bands at 3 000-3 750 cm 1 are respectively induced by H2O and hydronium. Comparing with the IR absorption spectra of the samples, it is indicated that the spectrum frequency bands with their positions are due to the isomorphism and chemical compositions in the different coloured tourmaline samples.