赞比亚墨绿色电气石的颜色成因初探

Colour Origin of Dark Green Tourmaline from Zambia

目前,对于绿色电气石的颜色成因仍存在争议。对赞比亚墨绿色电气石的不同方向和不同颜色区域进行LA-ICP-MS、电子探针以及偏振显微紫外-可见光谱测试,结果显示其化学成分以Al_2O_3和SiO_2为主,还含有一定量的FeO_T、MnO等杂质,其中Fe和Mn元素的质量分数较高;不同方向以及不同色带区域的微量元素的质量分数测试结果显示,赞比亚墨绿色电气石的墨绿色由Fe和Mn元素造成。偏光显微紫外-可见吸收光谱对不同色区及不同方向测试结果显示,都存在415,720nm处吸收带,其中415nm处吸收带主要与交换耦合Fe^(3+)—Fe^(3+)离子对的电荷转移、Mn2+的d电子跃迁吸收有关,720nm处吸收带主要与Fe^(2+)—Fe^(3+)离子对间的电荷转移跃迁有关。结果初步认为,赞比亚墨绿色电气石的主要致色成因是Fe和Mn元素致色。

A series of tests have been conducted on dark green tourmaline crystals from Zambia？including conventional characteristics, L A -IC P -M S , EPM A and m icroscopic polarizedU V -V is absorption spectra in order to fully understand their colour origin. Electron microproberesults indicated that, mass fraction of A120 3 and S i0 2 are high in the tourmaline samples,and a certain amount of FeOT ？M n O ,T i0 2 and Cr20 3 are contained, while FeOT is relativelyhigher. E PM A results showed the content of the trace element of different directionsand colour zones. Dark green area contains more content of Fe. M icroscopic polarized U V -Vis absorption spectra showed that all samples have strong absorption bands centered at415 nm and 720 nm. The absorption band near 415 nm is assigned to charge transfer betweenFe3＋-Fe3＋, as well as Mn2＋. The absorption band near 720 nm is usually ascribed to thecharge transfer between Fe2＋-Fe3＋. The intricate interplay between these two bands is the main cause of the colour that we observed.