Spectral Characteristics and Application of Synthetic Hydrothermal Red Beryl
DONG Xue1, QI Li-jian2, ZHOU Zheng-yu2, SUN Dui-xiong1*
1. College of Physics and Electronic, Northwest Normal University, Lanzhou 730070, China
2. School of Ocean and Earth Science, Tongji University, Shanghai 200092, China
Abstract：By using conventional gemological test methods, then combining the UV-Visible spectroscopy(UV-Vis) and Fourier transform of infrared spectral technology (FT-IR), this research focuses on the natural Utah red beryl and Russian hydrothermal synthetic red beryl, which are studied by the gemological characteristics, the UV-visible absorption spectrum, the mid-infrared absorption spectrum (MIR) and the near-infrared spectrum(NIR) characteristics. The results showed thatit is difficult to discriminate the natural red beryl and the hydrothermally synthesized red beryl through the conventional gemological test methods. Also, there is limited ability of UV-visible absorption spectrum to identify the natural and synthetic red beryl. At the same time, the mid-infrared absorption spectrum (MIR) of these two kinds of gems has no obvious difference. Their absorption position and absorption intensity are basically similar, which only show the vibration characteristics of the silicate crystal structure of beryl. As for spectrum of 2 000~9 000 cm-1 scope, there is obvious difference between the natural red beryl and hydrothermal synthesis red beryl. Therefore, the near-infrared absorption spectrum could be used as aunique identification characteristic to differentiate them. Further studies have shown that the natural red beryl sample contains little structural water. However, there exists a very weak absorption band between 3 300～3 600 cm-1 and this might be other forms of water in the natural red beryl sample. It could be concluded that the natural red beryl sample contains certain water, and it might be the channel water. The near-infrared spectrum characteristics of the hydrothermal synthetic red beryl samples show that it has strong water vibration absorption between 3 500~4 000 and 5 000~5 800 cm-1. There exist two types of water in the range of 5 000~5 800 cm-1, which include the weak absorption peak (type Ⅰ water) and the strong absorption peak (type Ⅱ water), which can be attributed to the combined vibration of flexural vibration and stretching vibration of water; the weak type Ⅰ water absorption peak and the strong type Ⅱ water absorption peak are also shown in the range of 7 000～7 500 cm-1, which can be attributed to the double frequency vibration of water. This means the hydrothermally synthesized red beryl is mixed with type Ⅰ structural water to type Ⅱ structural water. It could be concluded that the near-infrared absorption spectrum (NIR) characteristics of hydrothermal synthesis of red beryl samples in the range of 3 500~4 000 and 5 000~5 800 cm-1 can be used as the basis for distinguishing natural and hydrothermal synthesis of red beryl. According to whether or not the red beryl has water, the state of occurrence of water, and the relative intensity and frequency of different types of water, the UV-VIS spectroscopy, the mid-infrared absorption spectroscopy (MIR), and the near-infrared spectroscopy (NIR) can be used as an important basis for accurately providing diagnostic evidence for distinguishing natural and hydrothermal synthesis of red beryl.
