“重结晶”祖母绿的宝石学特征

Gemmological Characteristic of "Recrystallized" Emerald

  • 摘要: 近年来市场上出现了一种声称由天然祖母绿粉末重结晶而成的“重结晶”祖母绿。为了验证其真实性,在常规宝石学测试的基础上,采用激光剥蚀电感耦合等离子质谱仪、傅里叶红外光谱仪、紫外-可见分光光度计、激光拉曼光谱仪等测试仪器,从宝石学特征、化学成分及谱学特征对6件“重结晶”祖母绿样品进行研究。结果显示,“重结晶”祖母绿样品的内含物有黄铁矿、水波纹、气液两相包裹体、愈合裂隙等;其化学成分为w(Al2O3)=18.48%~18.79%,w(SiO2)= 65.93%~66.19%,w(Be)=49 700 ppm~50 700 ppm,微量元素具有富钒贫铁的特征;“重结晶”祖母绿样品的红外光谱有Ⅰ型水(5 102,5 456 cm-1)和Ⅱ型水(5 272 cm-1)处的吸收峰,且Ⅱ型水的吸收峰更强,与天然祖母绿中水的吸收峰位置不同;“重结晶”祖母绿样品的紫外-可见光谱一类有显示铬离子、铁离子和钒离子的吸收,另一类有显示铬离子和钒离子的吸收;拉曼光谱显示Be-O伸缩振动(1 067 cm-1处),Si-O-Si变形振动(683 cm-1处)和晶格振动(321.5 cm-1处),在683 cm-1处的半高宽均小于8.6 cm-1,和水热法合成祖母绿的谱峰一致。结果表明,“重结晶”祖母绿符合水热法合成祖母绿的多项特征,其中,含有黄铁矿的“重结晶”祖母绿样品可能是以含有黄铁矿的天然祖母绿作为种晶,其它样品未见指示天然成因的特征。所谓的“重结晶”祖母绿更多的是商家吸引顾客的噱头。

     

    Abstract: Recently, a kind of "recrystallized" emerald has appeared in the market. In order to validate its authenticity, on the basis of conventional gemmological testing, several testing instruments were used such as laser ablation inductively coupled plasma mass spectrometry, Fourier transform infrared spectrometer, ultraviolet-visible spectrophotometer, and laser Raman spectrometer. The gemmological characteristics, chemical compositions and spectroscopy characteristics of six "recrystallized" emerald samples have been discussed.The inclusions of the samples include pyrite, water-ripple pattern, gas-liquid two-phase inclusion, and healed cracks. The chemical composition of the sample is of w(Al2O3)=18.48%-18.79%, w(SiO2)= 65.93%-66.19%, and w(Be)=49 700 ppm-50 700 ppm. The trace elements are rich in vanadium and poor in iron. The infrared spectra of the samples shows absorption peaks of type Ⅰ water (5 102, 5 456 cm-1) and type Ⅱ water (5 272 cm-1), and the absorption peaks of type Ⅱ water were stronger, which were different from those of natural emerald. The ultraviolet-visible spectra of the samples shows absorption of chromium, iron and vanadium ions in one category, and absorption of chromium and vanadium ions in the other. Raman spectra of the samples show the Be-O telescopic vibration (1 067 cm-1), deformation vibration of Si-O-Si (683 cm-1) and lattice vibration (3 21.5 cm-1), with the FWHM of 683 cm-1 less than 8.6 cm-1, which is consistent with the spectral peaks of hydrothermal synthetic emeralds.The results show that the recrystallized emeralds accord with the characteristics of hydrothermal synthetic emeralds, among which, the samples containing pyrite may take the natural emeralds containing pyrite as seed crystals, and other samples have no characteristics indicating natural genesis. The so-called "recrystallized" emeralds are more of a gimmick to attract customers.

     

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