87 / 2019-10-10 10:44:46

“重结晶”祖母绿的宝石学特征

合成祖母绿,重结晶,水热法,内含物,红外光谱

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、傅立叶红外光谱仪、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六件“重结晶”祖母绿样品进行研究。
样品内含物有黄铁矿、水波纹、气液两相包体、愈合裂隙等。样品的化学成分含量为w(Al2O3)=18.48%~18.79%，w(SiO2)= 65.93%~66.19%，w(Be)=49700ppm~50700ppm，微量元素具有富钒贫铁的特征。样品的红外光谱有Ⅰ型水（5102cm-1、5456cm-1处）和Ⅱ型水（5272cm-1处）的吸收峰，并且Ⅱ型水的吸收峰更强，与天然祖母绿的水的吸收峰位置不同。样品的紫外可见光光谱一类显示铬离子、铁离子和钒离子的吸收，另一类显示铬离子和钒离子的吸收。样品的拉曼光谱显示Be-O伸缩振动（1067cm-1处），Si-O-Si变形振动（683cm-1处）和晶格振动（321.5cm-1处），在683cm-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。
Recently, a kind of "recrystallized" emerald has appeared on the market. In order to validate its authenticity, on the basis of conventional gemological 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 gemological characteristics, chemical composition and spectroscopy characteristics of six "recrystallization" 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)=49700ppm~50700ppm. The trace elements are rich in vanadium and poor in iron. The infrared spectra of the samples shows absorption peaks of type I water (5102 cm-1, 5456 cm-1) and type II water (5272 cm-1), and the absorption peaks of type II water were stronger, which were different from those of natural emerald. The uv-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 shows the Be-O telescopic vibration (1067 cm-1), deformation vibration of Si-O-Si (683 cm-1) and lattice vibration (321.5 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.