Abstract：In recent years, some low-temperature heated corundum has occurred in the gem trade market, which characteristics are similar to nature corundum. Therefore, how to distinguish low-temperature heated corundum has become a research hotspot in gem laboratories. In this paper, nine samples were treated at 360, 610 and 650 ℃ in a weak oxidizing environment, Micro-Raman spectrometer is used to determine the mineral inclusions, the microscope is used to observe the change of inclusions, and Micro-Infrared spectrometer is used to analysis of hydrous minerals and so on, to compare the characteristics of corundum before and after low-temperature heat treatment. Heat treatment reveals that around 600 ℃ temperature and weak oxidizing environment，the blue tone decreased and the red tone increased in the corundum, which could achieve the purpose of heat treatment to improve or change the color of the corundum. Hydrous minerals such as goethite, kaolinite and boehmite exist in the open fractures of corundum, diaspore, apatite and mica exist in the corundum crystal. FTIR absorption peaks of hydroxyl (—OH) differ from different minerals. Following is before heat treatment hydrous inclusion FTIR absorption spectra: goethite shows —OH related absorption peak in 3 435 cm-1 and absorption band center in 3 185 cm-1, kaolinite shows a group of absorption peaks in 3 620, 3 648, 3 670 and 3 698 cm-1, boehmite shows absorption peak in 3 086 and 3 311 cm-1, diaspore shows a peak in 1 980 and 2 110 cm-1, apatite shows a peak around 3 550 cm-1, and muscovite shows peak around 3 624 cm-1. After 360 ℃ heat treatment, related absorption peaks of —OH in goethite disappeared. After 610 ℃ heat treatment, related absorption peaks of —OH in kaolinite, boehmite and diaspore also disappeared, but the apatite peaks still exist. After 650 ℃ heat treatment, —OH related absorption peak in muscovite still exists. After heat treatment, goethite turns from yellow to red. Although diaspore has been dehydrated and phase changed, it still presents needle-like crystal pseudomorph. The crystal shape of apatite and muscovite has no change, and the transparency of muscovite is slightly reduced. The study provides that hydrous mineral inclusions are crucial to identify low-temperature heated corundum.
Key words：Low-temperature heated; Corundum; Hydrous mineral inclusion; Micro-Infrared spectrum
[1] National Gemston Testing Center（国家珠宝玉石质量监督检验中心）. Gems-testing（珠宝玉石名称）. Beijing: Standards Press of China(北京：中国标准出版社)，2017.
[2] GUO Zheng-ye，HAN Xiao-zhen，LIU Xue-liang, et al（郭正也，韩孝朕，刘学良，等）. Laser & Optoelectronics Progress（激光与光电子学进展），2015，52（8）：339.
[3] Vertriest W，Saeseaw S. Gems & Gemology，2019，55（44）：464.
[4] Hughes E B，Perkins R. Gems & Gemology，2019，55（2）：184.
[5] ZHANG Pei-li（张蓓莉）. Systematic Gemmology（系统宝石学）. Beijing：Geological Publishing House（北京：地质出版社），2006.
[6] Emmett J L，Scarratt K，McClure S F，et al. Gems & Gemology，2003，36（2）：84.
[7] HAN Xiao-zhen, KANG Yan, FENG Xi-qi，et al(韩孝朕，康 燕，冯锡淇，等). Journal of the Chinese Ceramic Society（硅酸盐学报），2019，47（7）：990.
[8] Sripoonjan T，Wanthanachaisaeng B，Leelawatanasuk T. The Journal of Gemmology，2016，35（2）：156.
[9] YANG Nan-ru，YUE Wen-hai（杨南如，岳文海）. The Handbook of Inorganic Matalloid Materials （无机非金属材料图谱手册）. Wuhan: Wuhan University of Technology Press（武汉：武汉工业大学出版社），2000.
[10] ZOU Xue-hua，CHEN Tian-hu，LIU Hai-bo，et al（邹雪华，陈天虎，刘海波，等）. Journal of the Chinese Ceramic Society（硅酸盐学报），2013，（5）：101.
[11] WEN Lu（闻 辂）. Infrared Spectroscopy of Minerals（矿物红外光谱学）. Chongqing：Chongqing University Press（重庆：重庆大学出版社），1989.
[12] ZHANG En，PENG Ming-sheng（张 恩，彭明生）. Mineral Resources and Geology（矿产与地质），2002，16（1）：41.
[13] LUO Min-hua，XU Qiong-qiong，ZHU Qing-xia（罗民华，徐琼琼，朱庆霞）. Chinese Ceramics（中国陶瓷），2007，43（4）：15.
