赞比亚Musakashi祖母绿的宝石学和谱学特征

Gemmological and Spectroscopic Characteristics of the Emerald from Musakashi, Zambia

  • 摘要: 与同属赞比亚的Kafubu祖母绿相比,Musakashi祖母绿具有独特的宝石学特征。本文选用14颗产自赞比亚Musakashi矿的祖母绿为研究对象, 利用常规宝石学测试仪器、激光拉曼光谱仪、红外光谱仪、显微紫外-可见-近红外光谱仪和激光剥蚀电感耦合等离子体质谱仪研究其宝石学特征。结果表明,Musakashi祖母绿样品的平均相对密度为2.65;在长波紫外灯下显示红色荧光,短波下呈惰性;内部较为干净,可见平行排列的长条状生长管、绿柱石和“莲藕状”包裹体;流体包裹体以多相为主,多呈锯齿状、长条状和矩形,气相为CO2和N2,液相为H2O,子矿物为岩盐和碳酸盐矿物;红外光谱表明,Musakashi祖母绿样品通道中的水分子以Ⅰ型水为主,在近红外区7 144、6 819 cm-1和5 105 cm-1处显示较强的吸收峰;紫外-可见-近红外吸收光谱表明,祖母绿样品的颜色主要受Cr3+影响;激光剥蚀电感耦合等离子体质谱分析表明,Musakashi祖母绿样品的化学成分特征表现为低Fe、Mg和碱金属元素,以及高Cr和V,通过绘制Li-K和Rb-Cs的二元对数投点图能够较好地区分产自Musakashi矿与世界上其他产地的祖母绿。

     

    Abstract: Compared with Kafubu emeralds from Zambia, emeralds from Musakashi possess unique gemmological characteristics. This study selects 14 emeralds from the Musakashi mine as subjects, examining their characteristics using conventional gemmological instruments, laser Raman spectrometer, infrared spectrometer, microscopic UV-Vis-NIR spectrometer, and laser ablation inductively coupled plasma mass spectrometry. Results indicate that the average relative density of the emerald samples from Musakashi, Zambia is 2.65. They exhibit red fluorescence under long-wave ultraviolet light, but inert under short-wave ultraviolet. The samples are relatively clean inside, featuring elongated growth tubes arranged in parallel, beryl and "lotus root" inclusions. The fluid inclusions are mainly multi-phase, presenting jagged, elongated, and rectangle shapes. The gas components include CO2 and N2, the liquid phase is consisted of H2O, and the daughter minerals including halite and a carbonate.Infrared spectra revealed that the water molecules within the emerald channels are primarily Type Ⅰ water, showing prominent absorption peaks at 7 144, 6 819 cm-1 and 5 105 cm-1 in the near-infrared spectrum. UV-Vis-NIR absorption spectra demonstrated that the colour of the emerald samples is predominantly influenced by Cr3+ ions. LA-ICP-MS analysis indicated that the Musakashi emeralds are characterized by low concentration of Fe, Mg, and alkali element, coupled with high Cr and V content. Binary log-log plots of Li versus K and Rb versus Cs content can distinguish the Musakashi mine from other significant emerald deposits worldwide.

     

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