Mineralogy and Spectra Study on Dougeng Stone from Shoushan, Fujian Province
XI Jia-xin1,2, CHEN Tao1*
1. Gemmological Institute, China University of Geosciences (Wuhan)，Wuhan 430074, China
2. Guangzhou Institute of Geochemistry，Chinese Academy of Sciences, Guangzhou 510640, China
Abstract：This paper studied main characteristics of Dougeng stone, by means of several Spectra methods like X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectra, as well as mineralogical methods like hydrostatic weighing method, scanning electron microscope (SEM) and liquid chemistry analysis. XRD result showed that the main mineral component of Dougeng stone was dickite, and the disintegration degree of the diffraction peaks and the strength of weak spectroscopie k≠3 represented the difference of the order degree of the sample dickite. Phase and polytype analyses showed that apart from dickite with 2M1 structure, there were also pyrite, alunite, pyrophyllite with a transition structure of 2M and 1Tc, and 2M1 illite. The analysis of the spectroscopies of the infrared spectrum showed that although there were differences in the order degree of samples, they all conformed to the infrared spectral characteristics of disordered dickite, according to peak position change and disintegration degree, which was consistent with the XRD test results. Since the microscopic characteristics of the sample section showed that the contents of the infected dark veins and opaque minerals in the sample had a significant influence on the appearance color of the sample, in-situ Raman spectroscopy was used to test the dark veins and opaque minerals. The results showed that the spectrum position, Raman shift and Raman scattering peak turned out to be typical spectral characteristics of FeS2, which meant that it was pyrite in the sample as the dark component played an important role in the color of Dougeng stones. The scanning electron microscope result revealed that the dickite particles were in microscopic cryptocrystalline-microcrystalline structure, appearing as pseudohexagonal platy, with local pyrite found to be microgranular in automorphic-semiheteromorphic structure in some samples. According to the results of chemical analysis and spectral analysis, the physical and mineralogical properties of Dengeng stones were correlated with the density, ordered measurement and the degree of uniform densification of internal microstructure; and there was a distinct origin of color in black Tianhuang stone or Kengtou stone in Shoushan and sample Dougeng stone, which had main chromogenic factor as impurity mineral pyrite with microcrystalline distribution (particle size ranging from 3 to 20 μm). Ferric ions in matrix dickite made less contribution to color rendering.
Key words：Dougeng stone; Dickite; Spectra; Mineral composition; Color genesis
席佳鑫，陈 涛. 福建寿山豆耿石的矿物学和谱学初探[J]. 光谱学与光谱分析, 2020, 40(04): 1179-1185.
XI Jia-xin, CHEN Tao. Mineralogy and Spectra Study on Dougeng Stone from Shoushan, Fujian Province. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(04): 1179-1185.
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