莫桑比克棕黄色碧玺的宝石学及光谱学表征

碧玺是晶体结构和化学成分都十分复杂的含硼硅酸盐矿物。在珠宝市场中最为常见的碧玺品种几乎都为锂碧玺和少量镁碧玺，目前的珠宝专业教材或相关领域的文章都对锂碧玺研究较多，而镁碧玺却少有涉及。对六颗产于莫桑比克的黄-棕黄色碧玺刻面宝石进行了宝石学常规测试、激光剥蚀电感耦合等离子体质谱（LA-ICP-MS）测试、红外吸收光谱、紫外-可见光吸收光谱、荧光光谱和激光拉曼光谱测试，以获得碧玺样品的宝石学及谱学特征。宝石学常规测试表明，实验样品与一般常见碧玺的物理和光学性质基本符合，但所有样品在紫外荧光仪短波（254 nm）下具有中-强绿色荧光，而一般碧玺在短波下为惰性，此外，样品中均含有较多的浅色和深色的粒状矿物包裹体，且不见一般碧玺中常见的长管状包裹体、气液两相包裹体。激光剥蚀电感耦合等离子体质谱（LA-ICP-MS）分析表明，实验样品属于镁碧玺，其平均晶体结构化学式为(Ca_0.15Na_0.85)_1.00(Mg_2.89Fe_0.02Al_0.09)_3.00Al₆(Si₆O₁₈)(B_0.95□_0.05O₃)₃(OH)₄。选取包裹体较少的样品进行红外吸收光谱测试，碧玺样品在2 000～6 000 cm-1区域内有OH和Si-O的振动峰，说明样品含有结构水。经过紫外-可见光吸收光谱测试，样品在400～500 nm内有一宽吸收峰，谱峰位置在445 nm左右，这可能与Fe2+-Ti4+的电荷转移和交换耦合的Fe2+-Fe3+离子对有关。经过荧光光谱测试，本批碧玺样品在254 nm激发光源下，产生中-强的绿色荧光，特征荧光峰为534 nm强峰及475 nm肩峰，荧光的产生原因与样品中Ti和Fe有关。对碧玺样品的主体矿物进行激光拉曼测试，测试结果符合镁电气石的拉曼光谱。该研究创新主要体现在以下两个方面：（1）研究对象经测试属于镁碧玺，其谱学特征方面尚未有详细研究；（2）实验样品在短波下具有独特的荧光现象，这一现象目前还没有其他学者提出，且笔者对荧光产生的原因进行了分析。

Gemological and Spectral Characterization of Brownish Yellow Tourmaline from Mozambique

Tourmaline is a borosilicate with complex crystal structure and chemical composition. The most common species of tourmaline on jewelry markets are elbaite and some dravite. There are numerous textbooks and articles in related fields focusing on elbaite rather than dravite. In this study, six light-yellow to brownish yellow tourmaline gemstones from Mozambique were examined. Standardgemological testing was followed by LA-ICP-MS, infrared spectroscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy and Raman spectroscopy testing. Standard gemological testing revealed that the physical and optical properties of the samples are basically in agreement with those of general tourmaline, but all samples have medium to strong green fluorescence under short-wave (254 nm) UV light, while general tourmaline is inert. In addition, the samples contain a lot of dark or grey granular mineral inclusions, but no tubular inclusions, gas-liquid two-phase inclusions, which are common in tourmaline. LA-ICP-MS testing shows that the samples belong to dravite and their average crystal structure formula is (Ca_0.15Na_0.85)_1.00(Mg_2.89Fe_0.02Al_0.09)_3.00Al₆(Si₆O₁₈)(B_0.95□_0.05O₃)₃(OH)₄. The samples with fewer inclusions were selected for infrared spectroscopy testing. The vibration peaks of hydroxyl group and Si-O are found in the 2 000～6 000 cm-1 region, indicating that the samples contain water. There is a broad absorption peak between 400～500 nm in the Ultraviolet-visible spectra. The peak position is about 445 nm, which may be related to the charge transfer of Fe2+-Ti4+ and exchange-coupled Fe2+-Fe3+. The samples emit medium-strong green fluorescence under 254 nm UV light. There are 534 nm strong peak and 475 nm shoulder peak in fluorescence spectra. The fluorescence may be related to the Ti and Fe in the samples. Laser Raman spectra of the tourmaline samples are performed. The result is in accordance with the Raman spectra of dravite (species of tourmaline). The innovation of this paper is mainly embodied in the following two aspects: (1) the samples turn out to be dravite, whose spectral characteristics have not been studied in detail. (2) These dravites have a unique fluorescence under short-wave UV light, which has not been documented, and the reason for the origin of the fluorescence has been deduced by the author.