Colour Origin of Green Chalcedony from Taiwan

Chemical compositions and spectral characteristics of green chalcedony from Taiwan, China, were studied with the help of UV-Vis-NIR spectroscopy, EPMA, XRD and IR spectroscopy. The distribution of its colour-causing element and colour-causing mineral were observed by EPMA, and the coloration mechanism of green chalcedony from Taiwan was concluded. The results showed that Cu in the tiny copper mineral chrysocolla causes the green colour. The UV-Vis-NIR spectra showed that the absorption band at 570-800 nm is caused by the²E_g→²T_2g spin allowed transitions of Cu²⁺. EPMA tests showed Cu in green chalcedony from Taiwan distributes unevenly and exists as impurity ion and copper mineral. The result of XRD showed that the copper mineral is chrysocolla. NIR spectrum showed the absorption peaks of chrysocolla and chalcedony, which further confirmed the existence of chrysocolla in green chalcedony from Taiwan.