Zultanite(变色水铝石)的宝石学及谱学特征

Zultanite(变色水铝石)是仅产自土耳其的奇异变色宝石。采用常规宝石学测试方法、傅里叶变换红外光谱仪、激光拉曼光谱仪、紫外-可见分光光度计和激光剥蚀电感耦合等离子体质谱仪等测试仪器分析变色水铝石的宝石学特征及谱学特征,并对其变色机理进行了探究。结果表明,变色水铝石样品的红外光谱主要由—OH和—OD的振动引起,其拉曼光谱主要由—OH和Al—O键的振动引起;变色水铝石样品的主要杂质元素有Fe、Si、Ti,还含微量的Ga、Cr元素;样品的紫外-可见光谱中Fe~(3+)的d—d电子跃迁与Fe~(3+)—Fe~(3+)离子对的跃迁共同作用引起371、385、397、448nm处的强吸收。Fe~(2+)—Ti ~(4+)的电荷转移与微量Cr~(3+)引起575nm左右的宽缓吸收。由此推断,变色水铝石的变色效应主要由Fe、Ti元素的综合作用导致,Cr元素影响微弱。

Gemmological and Spectral Characteristic of Zultanite:Colour-Change Diaspore

Zultanite, an exotic gemstone, is only found in (I) bir Mountains, Menderes Massif, Turkey as well as colour-change diaspore.In this paper, the authors studied the gemmological and spectral characteristics of Zultanite samples by means of conventional gemmological testing methods, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and ultraviolet-visible spectrometry (UV-Vis).The results indicated that the infrared absorption bands at 2 998、2 928 cm-1 are associated with-OH stretching vibrations.The infrared absorption band at 1 075 cm-1 is ascribed to-OH bending vibration, and 970 cm-1 is ascribed to-OH deformation vibration.Another two infrared absorption bands at 2 119、1 986 cm-1 are assigned to-OD stretching vibration.Raman bands at 1 192、1 048 cm-1 are associated with-OH bending vibrations, and 792、667、555 cm-1 are ascribed to-OH deformation vibration.The bands at 500、449、398、332、289、259 cm-1 are assigned to Al-O vibration.The most intense band at 449 cm-1 is ascribed to Al-O-Al bending vibration.The results of LA-ICP-MS test showed that the main impurity elements of Zulanite samples are Fe、Si、Ti with trace elements Ga and Cr.UV-Vis absorption spectroscopy analysis showed that four strong absorption bands at 371、385、397、448 nm are induced by d-d electronic transition of Fe3+ and charge transfer of Fe3+-Fe3+.The broad and weak band at 575 nm is induced by the charge transfer of Fe2+-Ti4+ as well as trace Cr3+, which the authors propose to be the main mechanism of colour change effect in Zultanite.