Mineralogical and Spectral Characteristics of Tanzanite
LAI Meng1，2，3, LIAO Zong-ting1，2，3, YANG Ru-zeng1，2，3, ZHOU Zheng-yu1，2，3*, ZHONG Qian1，2，3
1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
2. Shanghai Engineering ＆ Technology Research Center for Gem and Materials Technics, Shanghai 200092, China
3. Ocean and Earth Science School, Tongji University, Lab of Gem and Technological Materials, Shanghai 200092, China
Abstract：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.
Key words：Tanzanite; Spectroscopic characteristics; Color genesis; Mineralogical characteristics
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