Acta Petrologica et Mineralogica

Photochromism is the most significant and valuable optical characteristic in hackmanite. EDXRF, FTIR, UV-VIS-NIR, D65 standard light source, illuminator and colorimetry method were applied in this paper to study the decolortation efficiency of photochromism in hackmanite from Mogok, Myanmar (Burma). The results indicated that the major elements of hackmanite are Na, Al, Si, O, Cl and S, its trace elements should include Ca, K and Fe. There are three absorption peaks of 472, 540 and 667 nm in UV-VIS-NIR spectrum, with 540 nm having the strongest absorption peak. The peaks stay stable but their intensity decrease with time during decoloration. The absorption peak area of 540 nm is significantly negative corelated with time during 0～80 s (R²=0.99). The decoloration efficiency grows significantly when the luminance increases from 5 000 lx to 30 000lx. During decoloration, the lightness of hackmanite color increases, while its chroma decreases. The color parameter a^* decreases and b^* increase. Its hue turns from purple to pink slightly. All the color effect of photochromism in hackmanite is a direct result of charge transfer leading to the destruction of the F center in hackmanite.

hackmanite; photochromism; colorimetry; decoloration efficiency