Identification Characteristic of Dyed Haze Blue Turquoise

Recently, a type of gray-blue turquoise appeared on the market. Owing to its distinctive gray-blue hue, it is commonly referred to as haze blue turquoise in the trade. However, systematic research on its gemmological characteristics remains scarce. In this study, three natural and six treated haze blue turquoise samples were systematically compared by conventional gemmological tests, Fourier transform infrared spectroscopy, micro-laser Raman spectroscopy, X-ray fluorescence spectroscopy and ultraviolet-visible spectrophotometry. The results show that all treated haze blue turquoise samples were impregnated with organic resin, as evidenced by their relatively low specific gravity (2.22-2.62), and by the presence of organic resin-related vibrational peaks attributed to CH₂ stretching and bending vibrations in both infrared and Raman spectra. Raman spectra of some samples showed additional peaks at 2 149 cm^-1 and 2 086 cm^-1, which were assigned to -C≡N stretching and Fe²⁺-CN^- coordination vibrations, indicating that these samples had been dyed with Prussian blue. UV-Vis spectra of all treated samples showed a distinct absorption band centered at approximately 510 nm in the blue region, whereas this band was absent in natural samples. This absorption band was attributed to a colour enhancer (other than Prussian blue) added to the impregnating resin, and is considered key to the formation of the characteristic haze blue tone. Impurity minerals identified in the samples include quartz, anatase, and pyrite. In summary, the treated haze blue turquoise samples underwent organic resin impregnation combined with colour-enhancer tinting, with some samples additionally subjected to localized Prussian blue staining. Compared to their natural counterparts, the treated samples exhibited more vivid colouration.