坦桑石的矿物学及谱学特征研究

对来自坦桑尼亚Merelani地区的坦桑石样品，分别采用电子探针、EMXPLUS型ESR谱仪、同步热分析仪、紫外可见光谱仪以及傅里叶变换红外光谱仪进行了测试与分析。结果表明：坦桑石样品的主要成分为SiO₂，Al₂O₃和CaO，微量成分中V₂O₅含量相对最多，平均含量为0.36%；坦桑石样品本身不含吸附水，结晶水, 加热至780 ℃附近时，脱失结构水，样品中结构水大约占总质量的2%；ESR实验结果中显示出明显Fe3+和Mn2+的电子顺磁信号；紫外-可见光谱显示，样品在385 nm处出现吸收窄带，575和750 nm处分别出现较为宽缓的吸收；红外光谱测试表明，样品在6 500~9 000 cm-1波段的倍频振动区，基本没有吸收。在4 000~6 500 cm-1波段主要为和频振动，5 956 cm-1附近呈较宽缓的吸收峰，5 413，5 184，4 336和4 046 cm-1处出现较尖锐的吸收峰，主要可能由O-H，矿物内的Si-O，以及空气里面的H₂O分子和CO₂振动所引起。综合EPMA以及ESR分析结果，蓝-紫色坦桑石颜色可能主要由V3+和V5+共同引起，Fe3+晶体场的d-d电子跃迁、Fe2+→Ti4+的电荷转移辅助致色。

Mineralogical and Spectral Characteristics of Tanzanite

In this paper, the Tanzanite samples from Merelani Tanzania have been respectively tested and analyzed by electron probe, EMXPLUS ESR spectrometer; SDT, UV VIS spectrometer and Fu Liye transform infrared spectrometer. The results show that: the Tanzanite samples are mainly composed of SiO₂, Al₂O₃ and CaO, V₂O₅ has the content of 0.36%, which is the most trace components; TG-DTA curves show that there is no absorption water and crystal water in Tanzanite samples, when being heated to 780 ℃, the structural water is lost, the water in the samples is about 2% of the total mass; ESR results shows obvious Fe3+ and Mn2+ electron paramagnetic signal; UV Vis spectra shows that an narrow- band absorption appears at 385 nm while a wide- band absorption appears respectively at 575 and 750 nm; infrared spectra shows that there is no absorption in 6 500~9 000 cm-1 of the Tanzanite samples. The 5 956 cm-1 is a wide absorption peak, and there is a sharp absorption peak respectively at 5 413, 5 184, 4 336, and 4 046 cm-1, which are mainly caused by the O-H, the Si-O within in the minerals as well as H₂O and CO₂ inside the air environment. Based on the results of EPMA and ESR analysis, the color of blue-violet Tanzanite may be mainly caused by V3+ and V5+, d-d electron transition of the crystal field of Fe3+ and charge transfer of Fe2+ to Ti4+ to assist coloration.