俄罗斯富铁型水热法合成祖母绿特征研究

针对近期市场上出现的俄罗斯富铁型水热法合成祖母绿，采用电子探针、傅里叶变换红外光谱仪和紫外-可见光谱仪等测试分析方法，从化学成分、宝石学特征及谱学进行初步研究。结果表明，俄罗斯富铁型水热法合成祖母绿内部有特征的红棕色假六方片状金属固体包裹体，化学成分以贫碱富铁含铜为特征，环状分子通道内I型水和Ⅱ型水同时存在，在760nm处有由Fe3＋的d-d电子跃迁导致的特征吸收峰。除此之外，笔者对比分析了俄罗斯富铁型、传统水热法合成祖母绿、桂林水热法合成祖母绿、助熔剂法合成祖母绿及天然祖母绿样品在谱学上的差异。

Study on Characteristics of Iron-rich Hydrothermal Synthetic Emerald from Russia

Currently there appears a kind of iron-rich hydrothermal synthetic emerald which was made in Russia. The gemmological and mineral characteristics of this hydrothermal syn- thetic emerald are preliminarily researched by using conventional gemmological testing meth- ods and electron microprobe analysis （EPMA）, Fourier transform infrared spectrometer（FT- IR）, ultraviolet-visible spectrophotometer（UV-Vis）. The crystals of this hydrothermal synthetic emerald were classified as flat tabular crys- tals and there were some simple crystal forms, hexagonal prism, hexagonal bipyramid and pinakoid. The surface of the crystal was rough, and clear growth steps and growth hillock were observed on the surface. Seed crystal can also be found inside the crystal together with some tensional microfracture. Plumose microwavy lines were partial visible inside the crystal and some black or reddish brown pseudohexagonal metal inclusions were seen occasionally. The EPMA results indicate that the iron-rich hydrothermal synthetic emerald samples from Russia are characterized by poor alkaline, rich iron and content copper. The ω （FeOT） varies between 2.36%and 3.07%, the ω （Na20＋K20） is under 0.1%and there generallycontains trace amounts of cooper in the crystal. The FT-MIR spectra of the iron-rich hydrothermal synthetic emerald were resulted mainly from the cyclic silicate tetrahedron groups which were consistent with the standard atlas of the beryl. The FT-NIR spectra of the iron-rich hydrothermal synthetic emerald were mainly resulted from the channel-water, mineralizer and CO2. There were two types of H20 in channel of beryl at room-temperature： type-I Hz O and type-l] H2 O, with the vector of H--H perpendicular and parallel to the c-axis. The double-frequency vibration of type-I H20 and type- H20 were recorded from 7 400 to 6 800 cm-~ while the vibration at fundamental fre- quency was recorded from 4 000 to 3 500 cm-~ and the sum frequency of water was from 5 600 to 5 100 cm-1. There were shape bands at 7 143cm-~ （type- I ）and 5 273,3 605 cm-1 （type-II ）. So the iron-rich hydrothermal synthetic emerald from Russia was compound type with type- I and type- lI. The infrared absorption spectra caused by the mineralizer were re- corded at 3 221,3 159,3 110 and 2 326,2 242,2 144 cm-1 which can be considered to be an evidence of the genetic mineralogy. Studies on UV-Vis absorption spectra of the iron-rich hydrothermal synthetic emerald from Russia showed that the main absorption was caused by Cr3＋ ,Fd＋ and Fe3＋. We could observe some absorption bands at 427,600,637 and 684 nm, which were caused by Cr3＋ d-- d electronic transition. Two broad absorption centered at 372 and 451 nm, which was due to the forbidden transition of Fe3＋ （6 A1 -＊4 E （D） and 6 A~g.4 E14 As ）. In addition, a moderate band appears at 760 nm may be caused by the forbidden transition of Fe3＋ （6A1g_.4 T2g）and the absorption band had red shift with Fe increasing. What＇s more, the UV-Vis absorption spectra of the iron-rich hydrothermal synthetic emerald from Russia showed directional prop- erty that the absorption at 451 nm reached a maximum when it is perpendicular to the c-axis while the absorption at 956 nm reached a maximum when parallel to the c-axis. The differences between iron-rich hydrothermal synthetic emerald to different kinds of synthetic emerald and the natural emerald have been discussed.