Infrared and chemical characterization of natural amethysts and prasiolites colored by irradiation

Abstract

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 0 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.

Исследование Строения Поверхности Разрушения Гетерогенного Тела (Кварцевого Песчаника)

“…Она приписана молекулам воды, связанным друг с другом водородны-ми связями [17]. Максимумы 3310, 3435 и 3478 cm −1 приписаны валентным колебаниям OH в соединениях AlOH и LiOH, а 3620 cm −1 -в парах группировок SiOH в поверхностном слое кварца [18,19]. В спектре поверхности разрушения интенсивность этих максиму-мов увеличивается.…”

“…В них наблюдается три полосы: 2.4, 2.7 и 3.2 eV. Полоса 2.4 eV соответствует ≡ Si−O − , отрицательный заряд кислорода скомпенсирован ионами Li + , Na + или H + [18,19]. По-лоса 2.7 eV приписана самозахваченному экситону [20], а полоса 3.2 eV -отрицательно заряженному центру…”

Introductory Chapter: An Introduction to Trace Elements

“…In mineralogy, trace elements can substitute network-forming ions in mineral crystal structures; here, trace elements are not vital to a mineral's defined composition and do not appear in the mineral's chemical formula. However, as well known in the case of quartz, those metals occurring in trace quantities result in characteristic coloration of the minerals; for example, the substitution of silicon by iron in traces gives the quartz amethysts its famous purple coloration [5].…”

The Mössbauer spectra of prasiolite and amethyst crystals from Poland

“…This color is stable up to 600 °C. Color change in different quartz crystals caused by irradiation and heating has been demonstrated mainly with optical, FTIR and Raman spectra (Lameiras et al 2009;Guttler et al 2009;Hatipoğlu et al 2011;Alkmim et al 2013;Nunes et al 2013). Nassau and Prescott (1977) found the green and violet colors reflects structurally independent causes and the crystals to be different from "greened amethyst" as described in Lehmann and Bambauer (1973).…”