Abstract：Derived from ancient plants, ambers are the natural fossilized resins undergone a variety of geological reworking. Copal resins of lesser age and lower maturity are similar in appearance to ambers but semi-fossilized. Both copal resins and ambers are the products of fossilized processes of natural resins, and the chemical compositions of them bear typical characteristics of transitivity, over tapping and similarity, which makes the identification difficult. Recently copal resins from two origins are found in Chinese market. Borneo copal resins with brownish-red or brown appearance are easily mistaken for Burmese ambers, while Madagascar Copal Resins with faint yellow or golden color are confused with Baltic ambers. The market prices of copal resins and ambers with similar appearances vary considerably, which has aroused wide attention. Research objects were Borneo copal resins and Burmese ambers, Madagascar copal resins and Baltic ambers. Each category were selected 4 representative samples, a total of 16 pieces. Fourier-transform infrared (FTIR) spectroscopies were performed at the School of Gemology, China University of Geosciences in Beijing (CUGB). Using KBr pellet transmission method (100 mg KBr and 1.0 mg sample), mid-infrared (4 000~400 cm-1) spectra of investigated copal resins and ambers were obtained by a BRUKER TENSOR 27 FTIR spectrophotometer, with a resolution of 4 cm-1 and 16 scans each sample, at room temperature. Investigated Copal resins and ambers had distinct differences of shift and intensity of absorption peaks in the spectra, which might be used to rapidly identify them. The spectroscopic characteristics of Borneo copal resins were four absorption peaks in the region 3 000~2 800 cm-1, one strong absorption peak at 1 710 cm-1 and one shoulder peak at 1 730 cm-1, two weak peaks at 887 and 824 cm-1. The spectroscopic characteristics of Madagascar copal resins were three typical absorption peaks relevant to CC functional group, one strong absorption peak at 1 697 cm-1 and one shoulder peak at 1 724 cm-1, “W-shaped figure”composed by two absorption peaks at 1 271 and 1 176 cm-1. Burmese ambers similar with Borneo copal resins can be rapidly identified by the absorption peaks in the region 3 000~2 800 cm-1, one strong absorption peak at 1 724 cm-1，“W-shaped figure”in the region 1 300~1 100 cm-1. Baltic ambers confused with Madagascar copal resins can be rapidly distinguished by the typical figure of “Baltic shoulder”. In addition, R (A1 383 cm-1/A1 464 cm-1) value of Borneo copal resins are 0.823~0.860, greater than 0.605~0.643 of Burmese ambers. 0.900~0.985 of Madagascar copal resins were greater than 0.704~0.783 of Baltic ambers. R value can also be one of identification features. Domestic researches about ambers and copal resins were focused on GC-MS ClassⅠtype whose macromolecular structure were based on polymers or copolymers of labdanoid diterpenes. Previous research objects of copal resins were mainly from New Zealand and Colombia, lacking of Borneo and Madagascar copal resins. This research comparatively analyzed copal resins and ambers with similar appearances (Borneo copal resins and Burmese ambers, Madagascar copal resins and Baltic ambers), It revealed the infrared spectroscopic characteristics of Borneo copal resins and Madagascar copal resins and provided the scientific evidence to rapidly identify copal resins and ambers with similar appearances. Combined with previous studies, these research findings showed that infrared spectroscopy may have scientific significance for the classification of copal resins from different origins, as well as for the identification between confused copal reins and ambers.
代荔莉，施光海，袁 野，王美丽，王 妍. 婆罗洲和马达加斯加柯巴树脂红外光谱特征及其与外观相似琥珀的快速鉴别[J]. 光谱学与光谱分析, 2018, 38(07): 2123-2131.
DAI Li-li, SHI Guang-hai, YUAN Ye, WANG Mei-li, WANG Yan. Infrared Spectroscopic Characteristics of Borneo and Madagascar Copal Resins and Rapid Identification between Them and Ambers with Similar Appearances. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2018, 38(07): 2123-2131.
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