Comparative Study on Gemmological Characteristics and Luminescence of Colorless and Yellow Scapolites

Abstract

The orange fluorescence of scapolite has been confirmed to be caused by (S2)−, but the frequent blue fluorescence in gem-quality scapolite has not been well explained. An energy dispersive X-ray fluorescence spectrometer (XRF), electron probe microanalyzer (EPMA), X-ray powder diffractometer (XRD), Fourier transform infrared spectrometer (FTIR), Raman spectrometer, ultraviolet-visible spectrophotometer, fluorescence spectrometer, and conventional gemological test methods were used to study the gemological characteristics, chemical composition, coloration mechanism, spectral characteristics, and luminescence of colorless and yellow scapolite. The results show that both yellow and colorless scapolites are mizzonite and that they share the same gemological and spectroscopic characteristics. The results of XRD, FIRT, and Raman spectra show that the yellow scapolite has the same structure as the colorless scapolite. The yellow color of scapolite is caused by Fe3+ and when the Fe content is low it is colorless. Yellow scapolite has about three times the Fe content of colorless scapolite. Under the excitation of long-wave and short-wave ultraviolet light, scapolite forms a strong and wide excitation peak in the blue-violet region centered at approximately 410 nm, which is due to the 4f1 → 5d1 of Ce3+, resulting in blue fluorescence.