Spectral Characteristics of Two Kinds of Nanhong Agate Imitations
YANG Ling-yue1, YAN Sheng-wu2, 3, WANG Hao-tian1, ZHANG Yu-ting1, WANG Ren-yun4, YANG Ming-xing1, WANG Chao-wen1*
1. Gemmological Institute, China University of Geosciences (Wuhan), Wuhan 430074, China
2. Sichuan Institute of Geological Survey, Chengdu 610081, China
3. Key Laboratory of Sichuan Province for Evaluation and Utilization of Strategic Resources of Rare Metals and Rare Earth, Chengdu 610081, China
4. Liangshan Chuanliang Nanhong Agate Limited Liability Company, Xichang 615000, China
Abstract：The Nanhong agate is one of the most common red agates in the Chinese jewelry market. The market of the Nanhong agate is thriving, and Nanhong agate imitations are flourishing, while few studies have been conducted on the differences of materials and spectral characteristics between the natural Nanhong agate and its imitations. In this paper, the conventional gemological instruments, Microscope, UV-Vis spectrometer, Raman spectrometer and Fourier infrared absorption spectroscopy(FTIR) were employed to study two kinds of the Nanhong agate imitations and the natural Nanhong agate. The results show that the two kinds of the Nanhong agate imitations are both composed of quartz, similar to the natural Nanhong agate, and have a similar refractive index, density, hardness, color, luster, and other physical properties relative to the natural Nanhong agate, with inertia under both short-wave and long-wave ultraviolet light. The first imitation (FZP-1) imitates a cherry red bracelet, exhibiting a light orangey-red as indicated from the spectrum of the UV-Vis showing a broadened absorption band between 240 and 570 nm. The FZP-1 displays granular texture and a pulp luff-like shape, with red dyestuff filling along the edge of the quartz granular, a typical structural characteristic of a dyed quartzite. The second imitation (FZP-2) imitates a persimmon red bracelet with a yellow orange red color as demonstrated by an absorption band from 300，240 nm to 550，540 nm under UV-Vis. The natural Nanhong agate(TR) showed an absorption band from 440 to 560 nm under UV-Vis. The FZP-2 shows a cryptocrystalline structure, whose banded and nail-like structures can be observed on the surface, and whose different colors are shown in different layers, indicative of dyeing and heating treatments of the FZP-2. The nature Nanhong agate exhibits cryptocrystalline texture and contains spot-like hematite, which is remarkably different from the internal structures of two imitates. The FTIR spectrum reveals quartz’s typical spectrum characteristics for both of the two kinds of Nanhong agate imitations and the natural Nanhong agate. The absorption peaks existed in the range of 1 100～1 250 and 600～800 cm-1 are attributed to the So—O—Si’s asymmetric and symmetric stretching vibration, respectively. The peaks at 300～600 cm-1 are assigned to the bending vibration of Si—O—Si. The peaks around 800 cm-1 in FTIR patterns are splitting in both samples, indicating a good crystalline degree of quartz. Peaks between 2 800～3 200 cm-1 are detected at the particle clearance in the FZP-1 under micro-infrared spectroscopy, which is related to organic dyeing agent, especially at 2 916 and 2 848 cm-1 to the stretching vibration of C—H. In addition to the peak position of quartz, the Raman spectrum of the FZP-1 show peaks at 915 and 1 337 cm-1, due to the bending vibration of the saturated C—H, which are related to organic dyeing agent, in good agreement with the result of micro-infrared spectroscopy. The peak at 502 cm-1 in the Raman spectrum indicates the existence of moganite in the ZFP-2. The ratios of relative content of moganite and quartz are calculated spanning 0.15～0.16, based on the ratios of characteristic peaks of moganite and quartz in the Raman spectrum, which is higher than the natural Nanhong agate. Rather than, the peaks relate to hematite is inexistent in both of the two kinds of imitations. The first and second imitations should be named as dyed quartzite and agate, respectively, according to the national standard of Gems-Nomenclature.
杨凌岳，鄢圣武，王浩天，张雨婷，王仁云，杨明星，王朝文. 两类南红玛瑙仿制品的光谱学特征[J]. 光谱学与光谱分析, 2022, 42(03): 835-840.
YANG Ling-yue, YAN Sheng-wu, WANG Hao-tian, ZHANG Yu-ting, WANG Ren-yun, YANG Ming-xing, WANG Chao-wen. Spectral Characteristics of Two Kinds of Nanhong Agate Imitations. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(03): 835-840.
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