Spectral Characteristics and Color Genesis of Yellow-Green Prehnite
LI Can1, CHEN Jiang-jun2, WANG Wen-jie3, YIN Ke4*, ZHENG Hai-rong1*, LU Zhuo5, LIU Zhen-dong4, WANG Yi-ming4, YANG Yun-qi3, HAN Wen6, WANG Chao-wen3
1. School of Art, Qingdao Agricultural University, Qingdao 266109, China
2. Hubei Institute of Hydrogeology and Engineering Geology,Jingzhou 434020, China
3. Gemmological Institute, China University of Geosciences (Wuhan), Wuhan 430074, China
4. School of Earth Sciences, China University of Geosciences (Wuhan), Wuhan 430074, China
5. School of Jewelry, West Yunnan University of Applied Sciences, Tengchong 679100, China
6. National Gems & Jewelry Testing Co. Ltd., Beijing 100013, China
Abstract:Color is one of the important optical properties of gemstones, and it is also an important parameter affecting their quality and price. As a common jade variety, the complex structure, color ions, valence states and coordination of yellow-green prehnite have led to great controversy about its color genesis. In this paper, the species, valence, and coordination state of the main chromogenic ions of two typical yellow-green prehnite samples (light yellow-green sample LYG and dark yellow-green sample DYG) were investigated using modern analytical methods such as Fourier infrared absorption spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), laser-exfoliation-plasma mass spectrometry (LA-ICP-MS) and Mössbauer spectroscopy, which provides a scientific explanation for the color genesis of yellow-green prehnite. UV-Vis analysis indicates that both sample LYG and sample DYG showed obvious absorption bands at ~425 and ~585 nm, which were related to the electron leap of Fe3+oct and the charge transfer of Fe2+ch-Fe3+oct, respectively. Ultrafine parameter analysis of Mössbauer shows that the IS of Fe3+ in both sample LYG and sample DYG is 0.34 mm·s-1, and the QS values are 0.22 and 0.35 mm·s-1, respectively, both consistent with the characterization of Fe3+ in the octahedral ligand of prehnite. Sample LYG (IS=1.08 mm·s-1) and sample DYG (IS=1.07 mm·s-1) have similar IS values for Fe2+, both of which are consistent with the characterization of Fe2+ in octahedral coordination. However, the QS value of Fe3+ in sample DYG (QS=2.78 mm·s-1) is significantly higher than that of the light yellow-green sample LYG (QS=1.12 mm·s-1), suggesting that Fe2+ is in the distorted octahedron in the former structure. The content of Fe and the proportion of Fe2+ in sample DYG (4.04 wt%; 11.88%) are higher than those of the light yellow-green sample LYG (3.55 wt%; 5.27%), suggesting that the yellow-green color of prehnite may be related to the content of Fe and the proportion of Fe2+. The contents of V in sample LYG and the dark yellow-green sample DYG are 633 and 1 810 μg·g-1, respectively, indicating that V may contribute to the yellow-green color of prehnite. Still, its content is significantly lower than Fe, so the contribution to the color is much lower than Fe3+ and Fe2+. The present study not only identified the main chromogenic ion species (Fe) of yellow-green prehnite, but also determined the valence states (Fe3+ and Fe2+) and coordination states (octahedral coordination) of the chromogenic ions, which provides a solid theoretical basis for the quantitative study of the color of yellow-green prehnite.
李 灿,陈江军,王文杰,殷 科,郑海蓉,陆 卓,刘振东,王一铭,杨云淇,韩 文,王朝文. 黄绿色葡萄石的谱学特征及颜色成因[J]. 光谱学与光谱分析, 2024, 44(09): 2538-2544.
LI Can, CHEN Jiang-jun, WANG Wen-jie, YIN Ke, ZHENG Hai-rong, LU Zhuo, LIU Zhen-dong, WANG Yi-ming, YANG Yun-qi, HAN Wen, WANG Chao-wen. Spectral Characteristics and Color Genesis of Yellow-Green Prehnite. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2024, 44(09): 2538-2544.
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