老挝田黄石的宝石学与矿物学特征

运用静水称重法、X射线粉晶衍射仪、傅立叶红外光谱仪、全岩化学分析、环境扫描电镜、激光剥蚀等离子质谱等测试手段,对老挝田黄石的矿物学特征进行了研究.结果表明,老挝田黄石含有多种高岭石族矿物,并以地开石为主.Fe3+为老挝田黄石呈黄色的致色离子.样品中高岭石族矿物颗粒直径为3~5μm,呈假六方片状,表面平整,呈三维堆垛或叠瓦状紧密排列.样品中矿物颗粒越小,结晶程度越好,自形程度越高,样品的透明度越高.微量元素分析可对老挝田黄石与田黄进行产地区分.老挝田黄石中Ga元素的质量分数高于田黄,而Co、Rb、Ni等元素的质量分数明显低于田黄.Co-Ga、Rb-Ga、Ni-Ga元素的投点图能较好区分老挝田黄石和田黄.老挝田黄石样品表现出轻稀土元素富集、重稀土元素亏损的特征,且轻稀土元素的分馏明显.

Gemological and mineralogical characteristics of Laos Tianhuang Stone

In this paper, the authors studied the gemological and mineralogical characteristics of Laos Tianhuang Stone by means of hydrostatic weighing method, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), whole-rock chemical analysis, environmental scanning electron microscopy (ESEM) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results indicate that the samples are mainly composed of dickite which belongs to kaolinite group minerals. According to whole-rock chemical analyses, Fe is the main trace element contributed to Laos Tianhuang Stone. The size of particle and degree of crystallization of minerals are associated with the transparency of samples, and the samples with high transparency are usually small particles with high crystallization. A comparison of chemical compositions between Laos Tianhuang Stone and Tianhuang shows that the content of Ga in Laos Tianhuang Stone is higher than that in Tianhuang, whereas the values of Co, Rb, Ni are obviously lower than those in Tianhuang. The element content can be used to perform synthetic origin identification. Plots of Co-Ga, Rb-Ga, Ni-Ga can be used to distinguish Laos Tianhuang Stone from Tianhuang. Laos Tianhuang Stone is rich in light rare earth elements(LREE) and poor in heavy rare earth elements(HREE).