Mineralogical Characteristic of Turquoise and Variscite from the Fangshankou, Gansu Province

In recent years, an ancient turquoise mining site was discovered at Fangshankou, Dunhuang, Gansu Province. Studies of the turquoise from this site revealed that the mine also produced a substantial amount of variscite, both of which were important gem materials in antiquity. However, due to the similarity of colour and texture, many excavated variscite artifacts have been misidentified as"turquoise" when unearthed. Therefore, it is significant to set up a comparative study of the mineralogical characteristics of the turquoise and variscite from Fangshankou, Dunhuang, Gansu Province. On one hand, it helps clarify the origin characteristics of the turquoise from Fangshankou, offering a new scientific evidence for tracing the mineral sources of the turquoise artifacts unearthed in northwest China. On the other hand, it provides fundamental mineralogical data on variscite, which is crucial for the researches on ancient Chinese turquoise and variscite artifacts. Accordingly, this study employed polarized microscope, X-ray powder diffraction, and electron probe to examine the surface microstructure and mineralogical characteristics of the samples.The results indicated that the presence of the cyrilovite in the impurity minerals of turquoise from Fangshankou can serve as a diagnostic feature for its identification.Electron probe data showed that the turquoise contains relatively high FeO_T content, which may distinguish it from turquoise of the other mining areas. The variscite samples are characterized by high iron and low chromium levels. Moreover, significant differences in spectral characteristics and composition(such as P₂O₅ and CuO content) were observed between the two minerals. This research provides a basis for the future material identification of variscite artifacts.