Gemological and Spectral Characteristics of Mexican Red Blue Amber
ZHAO Tong1, WANG Ya-mei1,2, LIU Ling1, LI Yan1,3*
1. Gemmological Institute, China University of Geosciences (Wuhan), Wuhan 430074, China
2. Gem Testing Center, China University of Geosciences (Wuhan), Guangzhou 510145, China
3. Hubei Engineering Research Center of Jewelry, Wuhan 430074, China
Abstract：In recent years, Mexican blue amber has become popular and has an increasing market share. Red blue amber is one of the varieties of blue amber, it usually has a maroon oxide surface layer, and the inner amber has blue-green fluorescence under ultraviolet light, so it’s also called “red skin blue amber”. However, the red blue materials in Mexican amber are very scarce due to the limitation of the formation conditions. In this research, gemological characteristics and spectral characteristics of Mexican red blue amber were studied using gemological routine methods, microscopic observation, infrared spectroscopy and photoluminescence spectroscopy Mexican black skin amber was investigated as a comparison with red blue amber. The red skin of Mexican red and blue amber is often slightly transparent, and its interior is translucent to slightly transparent. The thickness of red skin is uneven, and it is composed of black dots wrapped and flowing. The red part shows weak to no fluorescence under long-wave ultraviolet, and the inside shows strong blue fluorescence. The FTIR absorption peaks at 1 723 and 1 233～1 046 cm-1 in the red part of the red blue amber are respectively caused by oxygen-containing groups C═O and C—O. The absorption peak caused by —CH3 is located at 2 928 cm-1. The oxygen-containing group C═O is the chromophore that makes red blue amber appears red. The absorption intensity ratio of the C═O peak and —CH3 peak of the red blue amber red part is about 4/5, and the inner part is about 2/5~1/2. The oxidation degree of the red part of red blue amber is stronger than the inner part, while the oxidation degree of red blue amber’s inside is higher than that of the black skin amber’s inside. Photoluminescence spectroscopy results show that the red part of red blue amber has different luminescence centers with the inner part. The luminescence centers of red part are located at 562 and 506 nm, while the inner part mostly emits 467 and 472 nm center. As the degree of oxidation increases, the luminescent center gradually shifts to red spectra region, and the fluorescence intensity is significantly decreases. C═O quenches the fluorescence of Mexican red blue amber. The inner part of the black skin amber has two wide luminescence centers of 489 and 466 nm. The fluorescence intensity of black skin amber inside is higher than that of red blue amber inside. This research provides a basis for the identification of Mexican red blue amber and is beneficial for readers to distinguish Mexican red blue amber from other origins and other varieties. It has important theoretical significance and market application value.
Key words：Red blue amber; Mexico; Infrared spectroscopy; Photoluminescence spectroscopy; Fluorescence
赵 彤，王雅玫，刘 玲，李 妍. 墨西哥红蓝料琥珀的宝石学及谱学特征[J]. 光谱学与光谱分析, 2021, 41(08): 2618-2625.
ZHAO Tong, WANG Ya-mei, LIU Ling, LI Yan. Gemological and Spectral Characteristics of Mexican Red Blue Amber. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2021, 41(08): 2618-2625.
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