Study of Mineralogical and Spectroscopic Characteristics of Black Nephrite from Dahua in Guangxi
PENG Fan1, ZHAO Qing-hua2, PEI Lei1, WANG Chao2, YIN Zuo-wei1*
1. Gemological Institute, China University of Geosciences, Wuhan 430074, China
2. Zhengzhou Vocational University of Information and Technology, Zhengzhou 450046, China
Abstract：In recent years, a large amount of black nephrites began to appear in domestic and foreign markets. A new kind of black nephrites was found in Dahua Yao Autonomous County, Guangxi Zhuang Autonomous Region. In order to analyze mineral composition, spectroscopic characteristics and chemical composition of Dahua black nephrites, the standard gemological methods, X-ray powder diffraction, laser Raman spectroscopy, infrared absorption spectroscopy and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) were used. Based on standard gemological testing, the samples showed a spot RI of 1.64 and a hydrostatic SG of 3.12. With polarizing microscope, the major constituent mineral for Dahua black nephrites is found to be actinolite(>98%). The main structure of samples is microstructure fibers woven structure. The major constituent mineral of samples is confirmed to be actionolite with XRD testing. The characteristic mesh spacing of actionolite is 8.498 3 and 3.145 9 . FTIR spectrum of samples are similar to that of tremolite, and main absorption bands are 1 078，1 026，925，765 ，703，659，584，485，436 cm-1. Infrared absorption bands at 1 078 ，1 026，925 cm-1 are induced by O—Si—O antisymmetric stretching vibration, Si—O—Si antisymmetric stretching vibration and O—Si—O symmetric stretching vibration. Infrared absorption bands at 765，703，659 cm-1 are induced with Si—O—Si symmetric stretching vibration. Infrared absorption bands at 584，485，436 cm-1 are induced with Si—O bending vibration. Laser Raman spectroscopy testing results show that Raman peaks of samples are located at 3 500～3 800 and 119～1 054 cm-1. Raman peaks at 1 055, 1 029 and 930 cm-1 are induced by Si—O stretching vibration which is the characteristic vibration of amphibole. Raman peaks at 744 and 671 cm-1 are induced by Si—O—Si stretching vibration. 671 cm-1 is the strongest Raman peak, which represents symmetric stretching vibration of bridge oxygen in silicon-oxy tetrahedron. Raman peaks in the range of 3 800～3 500 cm-1 are induced by M—OH stretching vibration. These Raman peaks reveal bonding vibration information between cations in M1, M3 and OH-. Raman peaks at 3 628，3 647，3 664，3 678 cm-1 are induced by OH- stretching vibration. According to LA-ICP-MS, the chemical compositions of samples are SiO2(52.4%)，FeO(21.95%), CaO(12.5%) and MgO(12.4%). A spot of Al2O3，MnO，Na2O，P2O5，K2O and TiO2 were found. Having high concentrations of Fe is a notable characteristic of Samples. The result of Mg/(Mg+Fe) is 0.504, suggesting that Dahua black nephrites belong to actinolite jade in nephrite series. High-Fe actinolite is responsible for the color of Dahua black nephrites.
Key words：Dahua；Black nephrite；Mineralogical characteristics；Spectroscopic characteristics；Mechanism of coloration
彭 帆，赵庆华，裴 磊，王 超，尹作为. 广西大化墨玉的矿物学及谱学特征研究[J]. 光谱学与光谱分析, 2017, 37(07): 2237-2241.
PENG Fan, ZHAO Qing-hua, PEI Lei, WANG Chao, YIN Zuo-wei. Study of Mineralogical and Spectroscopic Characteristics of Black Nephrite from Dahua in Guangxi. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2017, 37(07): 2237-2241.
