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Materials Research

Print version ISSN 1516-1439On-line version ISSN 1980-5373


LAMEIRAS, Fernando Soares; NUNES, Eduardo Henrique Martins  and  VASCONCELOS, Wander Luiz. Infrared and chemical characterization of natural amethysts and prasiolites colored by irradiation. Mat. Res. [online]. 2009, vol.12, n.3, pp.315-320. ISSN 1980-5373.

The infrared bands of amethyst and prasiolite samples from different origins were correlated to the trace elements contents. Amethysts have an iron content greater than 20 ppm and a low content of sodium and potassium. Prasiolites have an aluminum content greater than 120 ppm and a higher overall trace elements content, which accounts for a strong absorption between 3200 and 3600 cm-1. Colorless samples of quartz that become amethysts and prasiolites after irradiation have infrared spectra at room temperature with a broad band at 3441 cm-1 and a sharp band at 3595 cm-1. The broad band splits in several bands at low temperatures that are related to AlSi and FeSi. The color of amethysts and prasiolites are assigned to [AlSiO4/h+]º and [FeSiO4/h+]º centers formed by the exposure to ionizing irradiation and to the influence of lattice distortions due to the content of iron as a substitute for silicon and a high content of trace elements of large ionic radius like potassium.

Keywords : amethyst; prasiolite; infrared spectrum; irradiation; trace elements.

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