Influence of Heat Treatment on Colour of Amethyst and Its Spectral Characteristic
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摘要: 天然黄水晶颜色金黄，犹如黄金，深受人们的追捧，市场上常出现紫水晶经加热处理得到的黄水晶。主要选取市场上常见的几种不同色调的紫水晶，通过加热处理实验，确定紫水晶的变色温度，并结合显微镜下观察、红外光谱和紫外-可见吸收光谱测试发现：紫水晶经过热处理后改色成黄水晶，可通过颜色、光泽、内部包裹体及表面特征与天然黄水晶进行辨别；热处理过程中，紫水晶随着温度的升高而改变颜色，由紫色到无色到黄色，且变色温度(400～500℃)与恒温时间长短有关；经热处理后的紫水晶在红外光谱带中存在3 854、3 738、3 585、3 436、2 675、2 362、2 233 cm-1处吸收峰并没有消失，天然黄水晶则不存在特征的3 585 cm-1处吸收峰；紫水晶在紫外吸收光谱中540 nm处吸收强度随着温度的升高而降低。Abstract: Some salesmen often sell the heat treated amethysts for imitating the citrines in order to improve the price. In this paper, the amethyst samples with different purple were heated. The colour and spectral characteristics of amethyst samples before and after the heat treatment were studied by using the gem microscope, FTIR and UV-Vis spectrum. The authors found that the colour of amethyst samples became deeper and deeper when the temperature increased, which changed from purple to colourless to yellow at the temperature range of 400-500℃. And this colour-change temperature was related with holding time. The infrared spectrum of the amethyst after heat treatment with yellow colour had the absorption peaks at 3 854、3 738、3 585、3 436、2 675、2 362 and 2 233 cm-1. But natural citrine haven't the absorption peak at 3 585 cm-1. The intensity of UV-Vis absorption peak at 540 nm in amethyst sample, decreased when the temperature increased.
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Keywords:
- amethyst /
- citrine /
- heat treatment /
- FTIR /
- ultraviolet-visible spectrum
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