Iron K-Edge Xanes Study of Heated Green Beryl from Madagascar

Chawalit CHANKHANTHA, Panjawan THANASUTHIPITAK, Pinit KIDKHUNTHOD

Abstract


Rough green beryls from Madagascar were studied for their gemological characteristics after heat treatment. The conversion of the iron oxidation state after heating was studied using the modern technique of X-ray absorption spectroscopy. The X-ray absorption near edge spectroscopy (XANES) results are in conclusively agreement with the traditional Ultraviolet-visible-near infrared (UV-Vis-NIR) technique, where Fe3+ in an octahedral site is changed into Fe2+ after heat treatment. The undesirable yellow tinge in the stone, therefore, is expelled and, thus, an attractive blue color is developed. The green beryls contained moderate amounts of chromophore iron (up to 1.08 wt.% FeO(total)), and relatively low amounts of Cs and Na. Fourier transform infrared (FTIR) spectroscopic features and chemical analyses are consistent with alkali-poor beryl. The gemological characterization of Malagasy green beryl is also presented in detail.


Keywords


Beryl, heat treatment, UV-Vis-NIR, FTIR, XANES

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References


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