广西大化和贵州罗甸软玉的谱学特征及产地示踪研究

doi:10.3964/j.issn.1000-0593(2021)04-1294-06

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Abstract Nephrites from Dahua Yao Autonomous County, Guangxi Zhuang Autonomous Region and nephrites from Luodian County, Guizhou province have formed mining scales, both of which have many similar and different characteristics in gemology, spectroscopy and mineralogy. In recent years, a large number of nephrites from these two localities began to appear at domestic and foreign markets. In order to analyze spectroscopic characteristics and color-causing mechanisms of nephrites from these two different sources, the standard gemological methods including refractive index testing, hydrostatic specific gravity testing, an observation by the naked eye and gem microscope were used to their research gemological properties of them. Also, Fourier transforms infrared spectroscopy (FTIR), laser Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was also used to research spectral characteristics and chemical composition of these nephrites. The research result shows that the infrared spectrum of samples from Dahua County showed main absorption bands at 1 033，932，771，699，524，490 and 427 cm^-1, and Fourier transform infrared spectrum of Luodian nephrites samples mainly showed absorption bands at 1 032，932，773，700，525, 490 and 426 cm^-1. Infrared absorption bands at 1 033，1 032 and 932 cm^-1 are induced by O—Si—O anti-symmetric stretching vibration, O—Si—O symmetric stretching vibration and Si—O—Si anti-symmetric stretching vibration. Infrared absorption bands at 773，771，700 and 699 cm^-1 are induced by Si—O—Si symmetric stretching vibration. Infrared absorption bands at 525，524，490，427 and 426 cm^-1 are induced by Si—O bending vibration and M—O lattice vibration. Unlike previous studies, the absorption band at 850 cm^-1 is first discovered in Dahua nephrites, which may be attributed to minor amounts of diopside pyroxene in the sample. This absorption band has not been reported in the previous studies on Dahua nephrites. According to results of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), the main chemical compositions of nephrites samples from Dahua are SiO₂ (58.91%), MgO (25.77%) and CaO (13.67%). The main chemical compositions of Luodian nephrites samples are SiO₂ (57.07%)，MgO (24.85%) and CaO (17%). The average content of calcium in Luodian nephrites samples is a little higher than that of Dahua nephrites samples. A spot of FeO，MnO，Al₂O₃，Na₂O，K₂O，P₂O₅ and TiO₂ were also found in our samples. The value of Mg/Mg+Fe is 97.3% in Dahua and 98.8% in Luodian nephrites respectively. This means the main mineral composition of both location nephrites is tremolite. According to our research, Dahua nephrites and Luodian nephrites have different green color-causing mechanisms. Testing results of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) showed that the content of vanadium in Luodian nephrites samples increased with the green deepening, which showed that the color-causing ion of Luodian green nephrites is probably vanadium (V). This article discussed the green color-causing mechanism of Dahua nephrites for the first time. We think that chrome (Cr) and ion (Fe) are color-causing ions of Dahua nephrites because the content of chrome (Cr) and ion (Fe) increased with green deepening. The trace element values can be used to identify the location of the two site nephrites from Dahua and Luodian. Identifying a location tree can be used to distinguish all the known sites of nephrite in China now.

Key words：Dahua; Luodian; Nephrite; Spectral characteristics; Trac to the source

Received: 2020-10-22 Accepted: 2021-01-18

ZTFLH:

O657.3

Corresponding Authors: WANG Wen-wei, YIN Zuo-wei

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http://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2021)04-1294-06 OR http://www.gpxygpfx.com/EN/Y2021/V41/I04/1294