Acta Petrologica et Mineralogica

This paper presents a comparative study of the spectral characteristics of copal resins from six different origins: Russia, New Zealand, Borneo, Madagascar, Colombia, and Sumatra. The study uses gemstone microscopy, infrared spectroscopy, ultraviolet fluorescence observation, and three-dimensional fluorescence spectroscopy to identify the characteristics of the resins. The results indicate that the infrared spectra of Borneo and Sumatra copal resins are mainly characterized by four absorption peaks in the range of 3000~2800 cm^-1, absorption peaks at 1708 cm^-1 and a shoulder peak at 1732 cm^-1, a weak absorption peak at 888 cm^-1. Similarly, the main features of the infrared spectra of New Zealand copal resin are three absorption peaks in the range of 3000~2800 cm^-1 and weak absorption peaks at 1 642 and 888 cm^-1. The infrared spectra of copal resins from Madagascar, Colombia, and Russia exhibit similarities, with three combined characteristic absorption peaks associated with C=C, a strong absorption peak at 1 692 cm^-1, and two absorption peaks of comparable intensity at 1270 and 1180 cm^-1. Under long-wave UV fluorescence, the fluorescence intensity of Borneo and New Zealand copal is stronger than that of resins from other origins, but the fluorescence intensity of Borneo copal is significantly stronger and the fluorescence intensity of Madagascar copal is the weakest. Borneo and Sumatra copal resins emit three typical peaks at 445, 474 and 505 nm, which can be optimally excited by 416,447 nm. The strongest emission peak of New Zealand copal is at 385 nm, which can be best excited by 352 nm. The strongest emission peak of Russian copal is at 399 nm, which can be best excited by 354 nm. The strongest emission peak of Colombian copal is centered at 470 nm, which can be best excited by 400 nm; and the relative fluorescence intensity of Madagascar copal is the weakest, the strongest fluorescence peak is at 465 nm, which can be best excited by 378 nm. It was concluded that the fluorescence and infrared spectroscopic characteristics of the copal resin could provide a basis for the identification and classification of the resin.

copal resin; amber; three-dimensional fluorescence spectroscopy; infrared spectroscopy