• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.2
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• pp.73-77
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• 2004

The color enhancement for natural Zambian amethyst of low quality was carried out by the hydrothermal treatment method. The hydrothermal treatment conditions were as follows: reaction temperature; $300^{\circ}C$, duration; 30 hrs, filling; 40%, solvent; 6 M-HCI solution. The reddish purple amethyst of high quality was obtained under these conditions. From the result of ICP/AES, it was known that color enhancement was affected by a Fe elemental content to exist in the inside of natural Zambian amethyst. Also, from the result of UY-VIS-NIR, it was shown that the absorption peak at 550 nm after hydrothermal treatment is slightly lower than those of non-treated natural Zambian amethyst. In this study, it was known that hydrothermal treatment method was a way to suitable for increase of commercial value of natural Zambian amethyst.

• Journal of the Mineralogical Society of Korea
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• v.22 no.2
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• pp.97-106
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• 2009

It is known that the natural amethyst is changed to citrine after heat treatment. However, when all amethyst samples from Zambia were heat-treated in the temperature range of $350{\sim}380^{\circ}C$ for 1 hour, the result was that five out of eight samples were changed to citrine and all the rest of samples became rock crystal quartz. These differences in the color appearance seem to be influenced by the original colors contained in the amethyst before the heat treatment. The amethyst containing yellow color changed to citrine and the amethyst without containing yellow color changed to rock crystal quartz after the heat treatment. The results compared after the instrumental analysis on the difference of color change, it showed the differences of peak intensity in 3,400 $cm^{-1}$ and the existence and non-existence of peak at the range of 5,200${\sim}$5,400 $cm^{-1}$ in FTIR. It revealed the difference in the quantity of Cr which is a trace element in the WD-XRF analysis. The identical result in the FTIR spectra before and after the heat treatment reveals that the heat treatment did not cause any change in the main composing elements or crystal structure.