白色“淡水Akoya珍珠”和Akoya珍珠的谱学及成分特征

Spectrum and Chemical Composition Characteristics between White "Freshwater Akoya Pearls" and Akoya Pearls

  • 摘要: 近年来我国珍珠市场中出现了一类小颗粒(粒径3~10 mm)的优质的白色淡水有核珍珠,由于其与白色Akoya珍珠(简称Akoya)在外观上的相似性,被商家称为“淡水Akoya珍珠”(简称F-Akoya)。本文选取来自诸暨市场的F-Akoya及Akoya样品进行了常规宝石学测试、光致发光光谱测试、三维荧光光谱测试和LA-ICP-MS测试,对比分析得出了两类珍珠的的常规宝石学鉴定特征、谱学特征及成分特征,发现: (1)尽管它们外观相似,都具有强珍珠光泽和很高的正圆率,但Akoya珍珠层较薄,表面常有鱼鳞纹、褶皱,而F-Akoya珠层较厚,缺少鱼鳞纹;(2)PL光谱总体荧光强度(F)与文石主峰强度(A)的比值F/A值发现,F-Akoya通常在1~5范围内,远低于Akoya的13~169;(3)三维荧光光谱显示,F-Akoya的荧光光谱发光中心Ex/Em范围为350~380 nm/420~440 nm,且荧光强度很高,而Akoya的发光中心在350~400 nm/430~480 nm范围内,且荧光强度极低;(4)LA-ICP-MS测试发现,F-Akoya明显富Mn,而Akoya明显富Na、Mg、K、Sr,F-Akoya稀土模式为LREE相对HREE轻微富集,而Akoya则相反;(5)成分分析结果反映珍珠的微量和稀土元素含量与它们生长环境有关。通过三元成分图和稀土元素配分模式图,可以较好的区别两类珍珠。

     

    Abstract: In recent years, a kind of high-quality white freshwater nucleated pearls in small size (3-10 mm) has appeared in pearl market in P. R. China, which is commercially called "freshwater Akoya pearl" (F-Akoya) because of its similar appearance to white Akoya pearl (Akoya).In this paper, F-Akoya and Akoya pearl samples from Zhuji market were collected and analyzed by conventional gemmological test, photoluminescence (PL) spectrometer, three-dimensional fluorescence (3D FR) spectrometer and LA-ICP-MS. Although F-Akoya pearls are similar to Akoya pearls in appearance, they are clearly different in the following aspects: (1) In terms of the thickness and morphology of the nacreous layer, the Akoya is thinner with fish-scale-like grains and fold-like flaws on its surface, while the F-Akoya is thicker without fish-scales-like grains; (2) In terms of the F/A value, namely, the ratio of the overall fluorescence intensity (F) of the PL spectra to the main peak intensity of aragonite (A), the F-Akoya usually ranges in 1 to 5, much lower than the F/A range of Akoya(13 to 169); (3)In terms of the luminescence center Ex/Em in the 3D FR spectra, the F-Akoya ranges in 350~380 nm/420~440 nm with high fluorescence intensity, while the Akoya ranges in 350~400 nm/430~480 nm with low fluorescence intensity; (4) In terms of minor elements shown by LA-ICP-MS, F-Akoya is obviously rich in Mn, while Akoya richs in Na, Mg, K, Sr; (5) In terms of the rare earth element pattern, F-Akoya is enriched in LREE, while Akoya shows the opposite. The composition analyses revealed that the composition of the F-Akoya and Akoya depends on their growth water environment.Importantly, they can be distinguished by the ternary component diagrams and REE partition pattern diagram.

     

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