字很多 | Tokyo 惊现镀膜帕拉伊巴，动机不明

原文出处《GEMS & GEMOLOGY》 Spring 2017

原文作者Kazuko Saruwatari and Philip G. York

原文链接https://www.gia.edu/gems-gemology/spring-2017-cuprian-liddicoatite-tourmaline

【PS：网上那些翻译没什么毛病，但是图片并非来自GIA报告，也不是东京那颗帕拉伊巴，而是某位博主自己贴上去的】
【PPS：有些太专业的检测内容就不搬运啦】
【PPPS：这次镀膜并非改色，尚未明确其动机。我猜测是为了增加耐磨性or方便实验做的镀层。还要等后续报道】

        最近，GIA东京实验室收到一个镀膜（涂层）帕拉伊巴碧玺戒指样品（如图1），常规宝石学检测折射率为1.620～1.640，与碧玺一致；二色性中强，绿蓝色至浅蓝色；天然晶体包体及指纹状包体。拉曼光谱检测样品为碧玺，能量色散X射线荧光光谱（EDXRF）和紫外-可见光谱测试证明铜（Cu）为致色元素       
当样品戒指台面向上时，肉眼观察宝石很自然，但是，有镀膜（涂层）的表面在反射光源和暗场照明下看起来不同，在反射光下观察到铜黄色，不均匀的亚金属光泽（如图2）；而在暗光照射下，出现亚金属光泽区域的发白特征（如图3）。镀层（涂层）由于耐磨性较低，通常在面棱部位可以观察到磨损的痕迹。但本次样品的镀层（涂层）没有显示磨损的迹象，而且镀层（涂层）也不能用橡皮擦擦掉。
       使用激光烧蚀电感耦合等离子体质谱（LA-ICP-MS）对样品进行成分分析。可检测到如硼B，锂Li、钠Na等元素，证明样品为锂电气石。然而在样品的表面检测到电气石通常不含铂Pt，钨W和钼Mo元素，而且这些元素在近表面的浓度明显高于内部。我们几乎可以确定这种成分差异是由表面金属镀层（涂层）引起。金属铂Pt镀层（涂层）可能是为了用来提高宝石的耐磨性或者是为了方便扫描电镜（SEM）观察而做的样品处理。【对样品进行镀膜（涂层）的原因还不清楚，但这是GIA首次观察到此现象。】

贴一段：
Thirteen tourmaline samples of Paraíba-type colors (figure 1) from unknown geographic origins were examined in GIA’s Tokyo laboratory. These were submitted by different clients in 2016. Standard gemological testing was followed by analyses of the major, minor, and trace element concentration for each sample with LA-ICP-MS. Fluorine was not measured. A Thermo Fisher Scientific’s iCAP Qc ICP-MS was connected to an Electro Scientific Industries NWR213 laser ablation unit with a frequency-quintupled Nd:YAG laser (213 nm wavelength) running at 4 ns pulse width. NIST SRM 610 and 612 glass standards were used for external calibration. Ablation was achieved using a 40 μm diameter laser spot size, a fluence (energy density) of approximately 10 J/cm2, and a 7 Hz repetition rate. Three laser spots were acquired from the girdle of each sample. The composition was initially internally standardized with 29Si using a calculated amount of Si based on the weight percent of pure elbaite in the chemical formula. Twenty-six additional cuprian tourmaline samples submitted by clients were analyzed with LA-ICP-MS for comparison. Their geographical origin was identified using GIA’s tourmaline database. Eighteen of these additional samples were from Brazil, one from Nigeria, and seven from Mozambique.