Gemmological and Mineralogical Characteristics of Fluorite from Cuonadong, Xizang, China

The fluorite from the Cuonadong Be-Sn-W polymetallic deposit in Longzi County, Xizang, China, exhibits remarkable colouration. Previous studies on Be-Sn-W polymetallic deposits have yielded significant results, however, research on the gemmological characteristics of the fluorite from Cuonadong remains relatively limited. In this study, four fluorite samples from Cuonadong, Xizang, China were collected and analyzed using conventional gemmological test instruments, polarizing microscope, Fourier transform infrared spectrosmeter (FTIR), Raman spectrometer, ultraviolet-visible (UV-Vis) spectrosphotometer, X-ray fluorescence (XRF) spectrometer, and inductively coupled plasma mass spectrometry (ICP-MS). The results indicate that the fluorite samples contain numerous fluid inclusions and long columnar tremolite mineral inclusions.The samples are primarily composed of CaF₂ and contain rare earth elements (REEs) and metal elements. The total REE content (4.03-51.36 μg/g) is relatively low. Notably, the total REE content and the concentrations of La, Ce, Pr, Nd, Sm, Gd and Dy in green fluorite sample are significantly higher than those in other samples.The characteristic peaks of fluorite samples are evident in both infrared spectra and Raman spectra. Some samples exhibit photoluminescence peaks of rare earth ions in Raman spectra. Based on the chemical compositions and UV-Vis spectral characteristics, it is speculated that the green colouration of fluorite sample is primarily caused by Sm²⁺, with possible contributions from Y³⁺ and Ce³⁺.The deep pink colouration of fluorite sample is attributed to the YO₂ colour center.