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 synthetic emerald are preliminarily researched by using conventional gemmological testing methods and electron microprobe analysis(EPMA),Fourier transform infrared spectrometer(FTIR),ultraviolet-visible spectrophotometer(UV-Vis).The crvstals of this hydrothermal synthetic emerald were classified as flat tabular crystals and there were some simple crystal forms,hexagonal prism,hexagonal bipyramid and Dinakoid.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 resuits indicate that the iron-rich hydrothermal synthetic emerald samples from Russia are characterized by poor alkaline,rich iron and content copper.The w(FeO_T) varies between 2.36%and 3.07%,the w(Na₂O+K₂O)is under 0.1%and there generally contains trace amounts of cooper in the crystal. The FT-MIR spectra of the iron-ich 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 C0₂.There were two types of H₂O in channel of beryl at room-temperature:type-I H₂O and type-Ⅱ H₂O,with the vector of H-H perpendicular and parallel to the c-axis.The double-frequency vibration of type-I H₂O and type一Ⅱ H₂O were recorded from 7 400 to 6 800 cm^-1 while the vibration at fundamental frequency was recorded from 4 000 to 3 500 cm^-1 and the sum frequency of water was from 5 600 to 5 100 cm^-1.There were shape bands at 7 143cm^-1(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一Ⅱ.The infrared absorption spectra caused by the mineralizer were recorded 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 bv Cr³⁺,Fe²⁺ 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⁺(⁶A₁→⁴E(D) and ⁶A_lg→⁴E₁ ⁴A_g).In addition,a moderate band appears at 760 nm may be caused by the forbidden transition of Fe³⁺(6A_1g→⁴T_2g)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 property that the absorption at 45 1 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.