Spectral Study on Natural Seleniumin Turquoise From Shiyan, Hubei Province
KU Ya-lun1, YANG Ming-xing1, 2*, LIU Jia1, XU Xing1
1. Gemmological Institute, China University of Geosciences, Wuhan 430074, China
2. Gem Testing Center, China University of Geosciences, Wuhan 430074, China
Abstract：Recently, there is a kind of turquoise with gray black impurity in turquoise market of Hubei Province, which has been studied very little. This study selected a turquoise protolith from Shiyan, Hubei Province. Blue basal turquoise is covered with dark gray inclusions of different shapes and sizes. The magnified observation shows that dark gray inclusions minerals have a metallic luster. The dark gray inclusions have been measured by in situ micro-element analysis with LA-ICP-MS, phase observation with back scattering electron image, principal quantitative chemical composition analysis using EDS for semi-quantitative testing and EPMA for quantitative testing, and micro-laser Raman spectrometer testing. The test results show that: The LA-ICP-MS results of dark gray inclusion minerals are influenced by the diameter and depth of the laser ablation spot. The results show that the chemical composition is a mixture of dark gray inclusion minerals and a small amount of turquoise. Se in dark gray inclusion minerals content is 95 927～221 394 μg·g-1, which is obviously higher than that in blue basal turquoise (146～212 μg·g-1). The content of CuO in dark gray inclusion minerals is 7.47%～9.28%, the content of Al2O3 is 28.1%～35.7%, and the content of P2O5 is 30.1%～37.8%. In dark gray inclusion minerals CuO content is 7.47%～9.28%, Al2O3 content is 28.1%～35.7%, P2O5 content is 30.1%～37.8%, which are caused by a small amount of turquoise mixture. Backscatter electron images show that the crystalline particles of inclusion minerals are fine and mix with turquoise, and heteromorphic inclusion minerals are aggregates formed by multiple crystals. The results of EDS show that inclusion minerals mainly contain Al, P, Fe, Cu and Se. Quantitative analysis of principal chemical components by EPMA shows that inclusion minerals mainly contain Se, with a content of 79.34%～87.97%. In addition, due to the fine crystalline particles of inclusion minerals, in the aggregates, inclusion minerals are mixed with turquoise. Therefore, Al, P, Fe and Cu of turquoise can also be found in the quantitative determination of chemical composition. Al content is about 0.93%～4.13%, Cu content is about 1.30%～2.04%, P content is about 0.66%～2.40%, Fe content is about 0.31%. The micro-laser Raman spectra of inclusion minerals are sharp peaks at 144 and 235 cm-1. The inclusion mineral is mainly natural selenium, according to the results of chemical composition spectroscopy. Selenium minerals is a newly discovered inclusion mineral in turquoise. The discovery of natural selenium, an inclusion mineral in turquoise, can provide an effective basis for the identification of turquoise by jewelry practitioners.
Key words：Spectroscopic characteristics; Turquoise; Natural selenium; Chemical composition; Raman spectroscopy
库雅伦，杨明星，刘 佳，徐 行. 湖北十堰绿松石中杂质矿物自然硒的谱学研究[J]. 光谱学与光谱分析, 2021, 41(07): 2251-2257.
KU Ya-lun, YANG Ming-xing, LIU Jia, XU Xing. Spectral Study on Natural Seleniumin Turquoise From Shiyan, Hubei Province. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2021, 41(07): 2251-2257.
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