琥珀是古植物的液态树脂经过多种地质作用后形成的石化树脂。 柯巴树脂是形成年代较短且成熟度较低的半石化树脂, 其外观与琥珀较为相似。 柯巴树脂与琥珀都是天然树脂在石化过程中的产物, 两者的化学成分存在过渡、 重叠, 具有较多的相似性, 导致二者的鉴别有一定难度。 近期市场上出现两个产地的柯巴树脂, 其中棕红色-棕色的婆罗洲柯巴树脂常被误认为缅甸琥珀, 淡金色-金色的马达加斯加柯巴树脂常与波罗的海琥珀混淆, 已引起较为广泛的注意。 为此, 以外观相似的婆罗洲柯巴树脂与缅甸琥珀, 马达加斯加柯巴树脂与波罗的海琥珀, 为研究对象每类选取四块代表性样品, 共16块。 红外光谱测试在中国地质大学(北京)珠宝学院宝石研究实验室完成。 测试仪器为BRUKER TENSOR 27型傅里叶变换红外光谱仪, 扫描16次, 分辨率为4 cm-1, 扫描范围为4 000~400 cm-1, 室温。 研究结果显示, 外观相似的柯巴树脂和琥珀红外光谱吸收峰位置和吸收强度存在可识别的差异, 因此可以利用红外光谱特征对其进行科学有效的鉴别。 婆罗洲柯巴树脂的红外光谱主要特征为3 000~2 800 cm-1范围内的4处吸收峰和1 710 cm-1处较强吸收峰, 1 730 cm-1处肩峰、 887与824 cm-1处弱吸收峰。 马达加斯加柯巴树脂的红外光谱主要特征为与CC双键相关的3处组合吸收峰、 1 697 cm-1处强吸收峰, 1 724 cm-1处肩峰和由1 271与1 176 cm-1吸收峰组成的“W 图形”。 与婆罗洲柯巴树脂外观相似的缅甸琥珀可以通过3 000~2 800 cm-1范围内的2处吸收峰、 1 724 cm-1处强吸收峰、 1 300~1 100 cm-1范围内的一个“W图形”进行快速鉴别。 与马达加斯加柯巴树脂易混淆的波罗的海琥珀可以通过“波罗的肩”进行快速区分。 另外, 婆罗洲柯巴树脂R (A1 383 cm-1/A1 464 cm-1)值为0.823~0.860, 大于缅甸琥珀0.605~0.643; 马达加斯加柯巴树脂R值为0.900~0.985, 大于波罗的海琥珀0.704~0.783, 该值也可作为区分特征。 国内有关琥珀和柯巴树脂的研究主要为气相色谱质谱(GC-MS)划分的Ⅰ类琥珀和柯巴树脂(主要化学成分为半日花烷型双萜化合物的聚合物), 柯巴树脂针对新西兰和哥伦比亚这两个产地, 缺乏婆罗洲和马达加斯加柯巴树脂的红外光谱分析。 该研究对外观相似的婆罗洲柯巴树脂和缅甸琥珀, 马达加斯加柯巴树脂和波罗的海琥珀进行红外光谱的对比分析, 揭示了婆罗洲和马达加斯加柯巴树脂的红外光谱特征, 并为快速区分外观相似的柯巴树脂与琥珀提供科学依据。 结合前人研究, 认为红外光谱在不同产地柯巴树脂的分类及外观相似的柯巴树脂和琥珀的快速鉴别提供了重要的科学依据。

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.