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| Mineralogical and Spectroscopic Characteristics Comparison of Green Jadeite From Myanmar and Guatemala |
| TONG Zi-da, YAN Xiao-xu*, LIU Xi-feng, HE Rong-rong |
School of Jewelry, Guangzhou City University of Technology, Guangzhou 510800, China
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Abstract Gemstone jadeitite primarily consists of jadeite, other pyroxene minerals, and albite, among other minerals. It is widely renowned for its vibrant color, particularly its green hue. To address the lack of understanding of mineralogical characteristics and color mechanisms in green jadeitite, this study conducted EPMA, XPS, mid FTIR, and UV-Vis analyses on six specimens selected from Myanmar and Guatemala. The results revealed that the chromogenic minerals in the Myanmar samples were primarily pure Cr3+bearing jadeite or a combination of Cr3+ bearing, jadeite and omphacite. In contrast, the Guatemala samples consisted of pure Cr3+ bearing omphacite. Absorption peaks at 1 165 and 1 097 cm-1 were associated with jadeite and omphacite, respectively. Additionally, the Guatemala samples exhibited high levels of Ca and Mg but lacked Na, resulting in a shift of absorption peaks towards lower wavenumbers at 580, 526, 462, and 420 cm-1. Furthermore, they exhibited higher concentrations of Fe2+ and Fe3+, as indicated by narrow absorption bands at 330, 391, and 437 nm in the UV-Vis spectrum, which aided in distinguishing their origin from Myanmar. The combined results of UV-Vis and XPS attributed absorption bands at 380, 437, 636, 660, and 690 nm to the d—d orbital forbidden transitions of Fe3+ and Cr3+. In the Guatemala samples, absorptions at 333, 391, 437, and 640 nm were attributed to Fe3+-O2- charge transfer, Fe3+ d—d orbital spin-allowed transition, Fe3+ d—d orbital forbidden transition, and Cr3+ d—d orbital forbidden transition, respectively. Despite differences in chromogenic minerals between Myanmar and Guatemala, the color mechanisms were fundamentally similar, likely due to [AlO6] octahedral lattice isomophic substitution of Fe3+ and Cr3+, resulting in absorption bands in the ultraviolet (~380 nm) and violet-blue (380~450 nm) regions and broad absorption bands in the red region, leading to a transmission window in the green region. Notably, stronger absorptions in the violet-blue region in the Guatemala samples, indicated a grayish hue compared to the Myanmar samples.
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Received: 2024-04-07
Accepted: 2025-01-07
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Corresponding Authors:
YAN Xiao-xu
E-mail: yanxiaoxu@gcu.edu.cn
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