Gemmological and Spectral Characteristic of Afghanite

The afghanite is found in Badakhshan Province, Afghanistan, in 1968, which is quite different from the white "Afghan jade" on the market.The afghanite is a calcareous mineral like the feldspar. In this paper, the authors studied the gemmological and spectral characteristics of afghanite samples by means of conventional gemmological tests, X-ray diffraction(XRD), electron microprobe(EPMA), Fourier transform infrared spectrometer(FTIR), ultraviolet-visible absorption spectrometer(UV-Vis). The main mineral component of the afghanite samples is afghanite, containing trace davyne and liottite. In order to preliminarily study the colour forming mechanism of afghanite, ultraviolet-visible absorption spectrometer(UV-Vis) result showed that only blue light and a amount of red light are transmitted in the visible region (400-700 nm), thus showing the blue colour of afghanite. The absorption peak at 600 nm may be related to the transition of S^3-, and peak at 400 nm may be related to the charge transfer of S^2- and SO₄^2- ions. It indicated that the colour of afghanite is related to sulfur element.