Infrared Spectra of Grayish Green Nephrite and Gray Nephrite: Characteristics and Significance
REN Jian-hong1, SHI Guang-hai1*, ZHANG Jin-hong2, YUAN Ye1, GAO Kong1, WANG Mei-li1, LI Xin-ling3, LONG Chu4
1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geoscience, Beijing 100083, China
2. The World of Jade Museum & Exhibition Center, Sihui 526200, China
3. Xinjiang Uygur Autonomous Region Product Quality Supervision and Inspection Institute, Urumqi 830004, China
4. Guangdong Gemstones and Precious Metals Testing Center, Guangzhou 510080, China
Abstract：Grayish green nephrite is named for a kind of nephrite belonging to green nephrite type, but with appearance similar to gray nephrite. Although their appearance is similar, the price of grayish green nephrite is much higher than that of gray nephrite. Thus a phenomenon appears that some dealers tell their consumers green nephrite while selling gray nephrite. In addition, some jade materials with such appearance appear in some unearthed jade artifacts, but their types can not be accurately identified. This makes it particularly important to quickly and accurately identify grayish green nephrite and gray nephrite. In this study, representative grayish green nephrite and gray nephrite samples were investigated using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy and electron microprobe analysis, and all the characteristics were yielded. By comparing the features between them, it can be found that there is no significant difference in the UV-Vis reflection spectra of both types of samples. However, the differences in the infrared spectra of them are recognizable. In order to explore more effective identification features, the reflection and transmission methods were used to obtain infrared spectra. The infrared spectra of both types of samples were generally the same, with the following distinguishable differences. The peak or shoulder around 1 050 and 1 018 cm-1 and the broad shoulder near 411 cm-1 occur in the reflection spectra of grayish green nephrite which do not appear in those of gray nephrite. The shoulder around 453 cm-1 and the peak near 401 cm-1 exhibit in the transmission spectra of the gray which do not exist in those of the grayish green. The above findings can be used as spectral characteristics to identify grayish green nephrite and gray nephrite. The intensity of the OH stretching vibration bands at 3 674, 3 661 and 3 643 cm-1 after Beer-Lambert Law transformation of the infrared transmission spectra and the Mg and Fe2+ content in the M1 and M3 sites are well correlated. The Mg(M1+M3)# (Mg/(Mg+Fe2+) in the M1 and M3 sites) ratio calculated by the relationship between the above two can be used to distinguish between grayish green nephrite and gray nephrite using their infrared transmission spectra. Mg(M1+M3)# ratio in grayish green nephrite (0.871~0.892) is smaller than that of gray nephrite (0.927~0.949). Moreover, the result of electron microprobe analysis showed that there are some differences in chemical composition between them. Mg content in grayish green nephrite (4.45~4.53) is less than that of gray nephrite (4.66~4.78), and Fe2+ content in the grayish green (0.28~0.49) is larger than that of the gray (0.10~0.23). However, Mg and Fe2+ content between them are not much different from each other, suggesting that the difference in infrared spectra may be related to the physicochemical conditions during crystallization besides having a certain correlation with the composition (the genetic types of grayish green nephrite and gray nephrite are ultrabasic rock type and dolomitic marble type, respectively). The above infrared spectrum identification features not only have important gemological significance for identification of grayish green nephrite and green nephrite, but also have potential application value for discriminating origin and analyzing occurrence of some ancient jades with the similar appearance to the studied nephrites.
Key words：Grayish green nephrite; Gray nephrite; Infrared spectra; Identification
任建红，施光海，张锦洪，袁 野，高 孔，王美丽，李新岭，龙 楚. 青碧与青玉的红外光谱特征及意义[J]. 光谱学与光谱分析, 2019, 39(03): 772-777.
REN Jian-hong, SHI Guang-hai, ZHANG Jin-hong, YUAN Ye, GAO Kong, WANG Mei-li, LI Xin-ling, LONG Chu. Infrared Spectra of Grayish Green Nephrite and Gray Nephrite: Characteristics and Significance. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(03): 772-777.
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