Gemmological and Spectroscopic Characteristics of A Kind of Imitation of Agate from Yanyuan

Recently, a kind of imitation, whose appearance is very similar to that of agate from Yanyuan has appeared in the market. In order to determine its mineral components, chemical compositions and spectral characteristics, the conventional gemmological test methods, Fourier transform infrared spectroscopy(FTIR), Raman spectroscopy, X-ray fluorescence spectroscopy(XRF), ultraviolet-visible spectroscopy(UV-Vis) and other testing methods were used. The results show that the density of the imitation sample is greater than 2.70 g/cm³, and it can be easily scratched by a knife, and blistered by drops of hydrochloric acid. It has a fine structure, and has black dots of varying sizes sporadically distributed inside. Infrared spectra and Raman spectra show that it has the characteristic peaks of barite, calcite and epoxy resin. X-ray fluorescence spectra show that the main elements are Ba, Sr, S, which are consistent with barite. UV-Visible spectra show that the colouration of the pink part may be related to hematite, and the colouration of the yellow-green part may be related to the combined action of goethite and Cu^{2 +}, which is similar to the colouration mechanism of pink and yellow-green colours in natural agate from Yanyuan. Based on the analyses, this kind of "Yanyuan agate" is actually a mixture of barite, calcite and epoxy resin. In daily identification, it can be identified rapidly based on conventional gemmological features, and the spectroscopic features can help to further determine the mineral components of the imitation. According to GB/T 16553-2017 Identification of Jewelry and Jade, it is recommended that the terms "agate imitation" should be used instead.