Spectral and Typomorphic Characteristics of Quartzose Jade from Taishan, Guangdong Province
ZHANG Yue-feng, QIU Zhi-li*, CHENG Yin-ying, LI Zhi-xiang, LI Liu-fen, ZHU Ming
School of Earth Sciences and Engineering, Sun Yat-sen University, Guangdong Provincial Key Laboratory of Geological Process and Mineral Resource Exploration, Guangdong Provincial Key Laboratory of Geodynamic and Geological Hazards, Guangzhou 510275, China
Abstract：Quartzose jade, which is widely distributed and has been mined in more than 10 provinces and regions in China, is an important characteristic jade in the domestic market. It has been used for thousands of years and wasthe predominant jade material inthe pre-Qin period of Lingnan area. The origin distinction of quartzose jade is of great significance in gemology and archaeology. However, due to the similar appearance and composition characteristics for quartzose jades from different mines, there is still a lack of effective origin discrimination methods for quartzose jades, and the study on the origin typomorphic characteristics of quartzose jade is still very weak. Taishan jade, produced in Taishan, Guangdong Province, is a kind of quartzose jade increasingly valued for its Tianhuang-like appearance. On the basis of conventional gemological tests, the spectral characteristics and mineral composition of 6 representative samples of Taishan jade were studied by using X-ray powder diffraction spectrometer (XRD), Fourier transform infrared spectrometer (FTIR) and Raman spectrometer. The results showed that the main mineral of Taishan jade is quartz and the minor mineral is dikite or kaolinite, with other minerals spectroscopycally undetectable. The two kinds of kaolin group minerals do not coexist in Taishan jade. Based on the XRD-Rietveld quantitative analysis, the content of quartz in Taishan jade is less than 85 Wt%, while the content of kaolin group mineralsis between 17 Wt% and 36 Wt%. The absence of 502 cm-1 band, which is the diagnostic Raman band for moganite, in the Raman spectra of Taishan jade indicates that the quartz in Taishan jade has a higher crystallinity than the quartz formed at low temperature, such as chalcedony and agate. Taishan jade can be divided into two types: dickite quartzose jade (the main type) and kaolinite quartzose jade (the secondary type). The infrared spectra of dickite quartzose Taishan jade showed three intense OH-stretching bands at 3 622, 3 653 and 3 703 cm-1, while the Raman spectra showed similar bands at 3 622, 3 644 and 3 706 cm-1, both of which had the characteristics of obvious band splitting and the decrease of peak intensity toward high frequency. There were four OH-stretching bands observed at 3 620, 3 652, 3 670 and 3 695 cm-1 in the infrared spectra of kaolinite quartzose Taishan jade, and another four similar bands found at 3 620, 3 651, 3 670 and 3 687 cm-1 in the Raman spectra, of which the 3 670 cm-1 band was very weak and difficult to identify. The occurrence of well-ordered dickite and kaolinite in Taishan jade indicated that the Al-rich minerals in its protolith have undergone the metasomatic alteration of intermediate-temperature acid hydrothermal solution, and the metallogenic conditions are different from those of quartzose jade such as Huanglong jade, Jinsi jade and Huoshan jade. It can be confirmed that the dickite and kaolinite are the fingerprint minerals of Taishan jade, which are different from quartzose jades from other origins. The results in this study provided an important scientific basis for the origin tracing of Taishan quartzose jade and will be potentially used as a reference for the distinction of quartzose jades from different origins and the provenance study of ancient quartzose jade artifacts in China.
Key words：Quartzose jade; Mineral spectroscopy; Dickite; Kaolinite; Typomorphic characteristics
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