水热法合成蓝绿色绿柱石的宝石学及光谱学特征

doi:10.3964/j.issn.1000-0593(2021)07-2258-05

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Abstract In this paper, for a new blue-green hydrothermal synthetic beryl on the market, the systematic research is conducted by using LA-ICP-MS, IR spectrum, Raman spectrum, UV-Vis absorption spectrum to obtain the gemology and spectroscopic characteristics and to analyze the causes of colour, and provide reference data for testing institutions to identify such synthetic gems. The results show that the sample’s refractive index is 1.570~1.576, which is similar to natural beryl. All sample have a characteristic water ripple growth texture inside, which can be used as one of the main identification characteristics of this synthetic beryl. LA-ICP-MS analysis showed that the synthetic beryl’s chemical composition is relatively single, the main chromogenic elements are Cr and Ti, and also contains trace amounts of V, and the alkali metal content is extremely low. The UV-Vis spectrum mainly shows the absorption peak of Cr, combined with the LA-ICP-MS test results, it is believed that Cr and Ti mainly cause the blue-green tone. The Cr mainly causes the green tone, and trace V may also affect the green tone. Titanium causes purple, superimposed with green to form the blue-green hue of the sample. The specific color mechanism needs to be further studied. In the infrared spectrum of 2 000~4 000 cm^-1, the broad absorption band centered at 3 700 cm^-1absorbs strongly, which belongs to the fundamental frequency vibration and coupling of two channel water types. Peaks at 2 449, 2 615, 2 746, 2 813, 2 885, 2 983 cm^-1are caused by Cl^-；The strong absorption peaks of 3 108 and 3 299 cm^-1are caused by NH⁴⁺. The near-infrared absorption spectrum of 4 000~8 000 cm^-1, it is the combined frequency and frequency doubling vibration area of the channel water in synthetic beryl. Among them, the strongest absorption peaks at 5 275 cm^-1, accompanied by the stronger absorption peaks at 5 455 and 5 106 cm^-1caused by the combined frequency vibration of type I water, and the strong absorption peak at 7 143 cm^-1caused by frequency doubling vibration of type I water can be used as an important identification feature of hydrothermal synthetic beryl and is particularly important for the identification of thick faceted gemstones. The corresponding absorption peaks in natural beryl are weak or even absent. The Raman spectrum of the sample is the same as that of standard beryl. The half-height width of the 685 cm^-1 peak is 7.1～7.3 cm^-1, less than 8.5 cm^-1, which can be used as another identification feature of this hydrothermal synthetic beryl.

Key words：Synthetic beryl；Hydrothermal method；UV-Vis spectrum；IR spectrum；Raman spectrum

Received: 2020-06-23 Accepted: 2020-10-29

ZTFLH:

P575.4

Corresponding Authors: PEI Jing-cheng E-mail: peijc@cug.edu.cn

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http://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2021)07-2258-05 OR http://www.gpxygpfx.com/EN/Y2021/V41/I07/2258