Study on Chemical Compositions and Infrared Absorption Spectra of Natural and Synthetic Emeralds
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摘要: 祖母绿是一种高档名贵的宝石，其矿物学名称为绿柱石，化学成分为铍铝硅酸盐。鉴别天然祖母绿和人工合成祖母绿，已成为祖母绿宝石鉴定中的一个重要课题。文章采用常规宝石学研究方法、激光剥蚀-电感耦合等离子体质谱法和红外光谱技术对天然祖母绿 (包括哥伦比亚祖母绿和巴西祖母绿)、合成祖母绿 (包括助熔剂法合成祖母绿和水热法合成祖母绿) 样品进行了系统的分析和研究。结果表明，天然祖母绿与合成祖母绿的主要致色微量元素Cr的含量越高，祖母绿的绿色越浓艳；天然祖母绿与合成祖母绿的红外吸收光谱特征具有明显的差异；根据祖母绿中是否含水、水的赋存状态以及氯的吸收峰，可作为准确鉴别天然祖母绿和合成祖母绿的重要依据。等离子体质谱法化学成分分析不能确定祖母绿是天然形成还是人工合成，需在常规宝石学检测的基础上，综合研究祖母绿的红外吸收光谱特征及内含物特征，才能准确地鉴别天然祖母绿、水热法合成祖母绿和助熔剂法合成祖母绿。Abstract: As a top-grade and rare gemstone, emerald is a variety of the mineral beryl with the chemical composition Be3Al2 (SiO3)6. It is a significant research project to identify natural emerald as opposed to synthetic emerald. The routine gemological methods, laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) and Fourier Transform Infrared Spectroscopy (FTIR) absorption techniques were used to study natural emeralds from Colombia and Brazil and synthetic emeralds made by flux-grown and hydrothermal synthetic methods. The green color of emerald was closely related to the concentration of the trace element Cr (Ⅲ). The infrared absorption spectra characteristics indicated obvious differences between natural and synthetic emeralds. This technique can provide important information for identifying natural and synthetic emeralds, combined with the existing state of water and the absorption peak of chloric ion in emeralds. Chemical compositions obtained by LA-ICP-MS alone cannot differentiate between natural and synthetic emeralds. Therefore, combining the data with routine gemological methods, infrared absorption spectrum characteristics and inclusion characteristics are essential for distinguishing between natural and synthetic emeralds.
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