Comparison of Synthetic Colourless Sapphire and Natural Light-Coloured Sapphire
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摘要: 近来提拉法合成刚玉晶体可重达近百公斤。先进合成工艺生产出的无色刚玉内几乎不见弧形生长纹和拉长气泡。该合成品可以加工成刻面宝石，但目前还没有进入珠宝市场，可以预见在不久的将来会有大批量的该合成品或相似品出现。通过对该类合成无色蓝宝石和天然浅色蓝宝石的特征进行对比研究，发现二者的常规宝石学特征、紫外-可见光-近红外光谱特征相似，难以区分。但包裹体特征观察很有效，天然浅色者几乎都有晶体包裹体、愈合气液包裹体等，而合成者几乎无任何包裹体。当天然无色蓝宝石无瑕时，区分有难度，需要运用其它测试方法。红外吸收光谱和DiamondviewTM可以用来鉴定二者，阴极发光显示微弱的鉴别特征，可作为辅助鉴定依据。市场交易需要警惕合成无色刚玉的出现。Abstract: Recently Czochralski synthetic colourless corundum crystals can grow as heavy as one hundred kilograms.Such corundum crystal almost does not contain any inclusion as commonly seen in coloured synthetic ones with curved striae and elongated bubbles.The crystal can be cut and used as facet，which is similar to the appearance of natural colourless or lightcoloured sapphires.By far，such crystals have not yet appeared on the jewellery market. However，it is likely these synthetic or similar products will appear soon.By studying features between synthetic colourless sapphires and natural light-coloured ones，the authors find it is difficult to distinguish them by conventional gemmological methods and UV-Vis-NIR spectrum.Cathodoluminescence results show weak identification features.In terms of the non-destructive identification，visible inclusions are key features for separating the natural light-coloured sapphires from the synthetic colourless ones.Almost all the former ones have natural inclusions such as crystal inclusions and healing fluid inclusions，whereas the latter ones do not have any inclusions. However, if a colourless one is flawless, distinction features between them are difficult to be observed, In this case, results of infrared absorption spectrum, DiamondviewTM and cathodoluminescence seem to be useful tools for identification. Gem inspectors should be alert when meeting light-coloured sapphire without any visible inclusion.
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Keywords:
- corundum /
- synthetic sapphire /
- identification
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