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![](./images/clear.gif) 1.- Amethyst geodes in the basaltic flow from Triz Quarry at Ametista do Sul (Rio Grande do Sul, Brazil); magmatic source of silica for the amethyst crystallizations
Cambridge University Press; London; GBR; United Kingdom, 2007
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![](./images/clear.gif) 2.- Amethyst-bearing lava flows in the Parana Basin (Rio Grande do Sul, Brazil); cooling, vesiculation and formation of the geodic cavities
Cambridge University Press; London; GBR; United Kingdom, 2007
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