Color Change of Green Tourmaline from Madagascar by Heat Treatment
Abstract
Tourmaline is one of the most popular of semi-precious gemstones, because of its multicolour nature. In this research, color change and spectroscopic characteristics of green tourmaline from Madagascar, when subjected to heating in air atmosphere with heating temperature at 400-600°C, has been studied by EDXRF, UV-visible spectroscopy and diffuse reflectance infrared spectroscopy. CIE L*a*b* color measurement was employed to study the color change of green tourmaline via UV-visible spectrometer. The results revealed that the green tourmaline changed to yellowish green color after heating at 400-600°C. However, the lightness of heated sample was increased with heating at 400-500°C while that was decreased when the heating temperature was 600°C. The UV-visible spectra showed characteristic absorption bands due to Mn2+ and Fe2+. The band related to yellow and green color in the unheated and heated tourmalines. The diffuse reflectance infrared spectrum of green tourmaline revealed absorption bands of OH, BO3, Si6O18, and SiO at 3450, 1350, 1100 and 1085 cm-1, respectively. After heat treatment, their bandwidths in the range 400-2000 cm-1 and the O-H bond absorption band of water molecules also decreased. The results may be utilized to improve the color or clarity in the tourmaline. Keywords : tourmaline, green tourmaline, Madagascar, color change, heat treatmentReferences
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Kaewtip, M., and Limtrakun, P. (2016). Gemological and chemical characteristics of green tourmaline from Madagascar, Mozambique and Tanzania. Walailak Journal of Science and Technology, 13(12),
985-992.
Maneewong, A., Seong, B.S., Shin, E.J.,Kim, J.S., and Kajornrith, V. (2016) Color change of tourmaline by heat treatment and electron beam irradiation: UV-Visible, EPR, and mid-IR spectroscopic analyses. Journal of the Korean Physical Society, 68(1), 83-92.
Reddy, B. J., Frost, R.L., Martens, W. N., Wain, D. L., and Kloprogge, J.T. (2007). Spectroscopic characterization of Mn-rich tourmalines. Vibrational Spectroscopy, 44, 42-49.
Zolotarev, A. A., Frank-Kamenetskaya, O. V., and Rozhdestvenskaya, I. V. (2007). Crystallochemical formulas and definition of species of tourmaline-group minerals. Geology of Ore Deposits, 49 (7), 547–553.
Castaneda, C., Oliveira, E. F., Gomes, N., and Pedrosa Soares, A. C. (2000) Infrared study of OH site in tourmaline from the elbaite-schorl series. American Mineralogist, 85, 1503-1507.
Castaneda, C., Eeckhout, S.G., Costa, G.M., Botelho, N.F., and Grave, E.D. (2006) Effect of heat treatment on tourmaline from Brazil. Physics and Chemistry of Minerals, 33, 307-16.
Dirlam, D.M., Laurs, B.M., Pezzotta F., and William, B. (2002). Liddicoatite tourmaline from Anjanabonoina, Madagascar. Gems & Gemology, 38, 28-53.
Kaewtip, M., and Limtrakun, P. (2016). Gemological and chemical characteristics of green tourmaline from Madagascar, Mozambique and Tanzania. Walailak Journal of Science and Technology, 13(12),
985-992.
Maneewong, A., Seong, B.S., Shin, E.J.,Kim, J.S., and Kajornrith, V. (2016) Color change of tourmaline by heat treatment and electron beam irradiation: UV-Visible, EPR, and mid-IR spectroscopic analyses. Journal of the Korean Physical Society, 68(1), 83-92.
Reddy, B. J., Frost, R.L., Martens, W. N., Wain, D. L., and Kloprogge, J.T. (2007). Spectroscopic characterization of Mn-rich tourmalines. Vibrational Spectroscopy, 44, 42-49.
Zolotarev, A. A., Frank-Kamenetskaya, O. V., and Rozhdestvenskaya, I. V. (2007). Crystallochemical formulas and definition of species of tourmaline-group minerals. Geology of Ore Deposits, 49 (7), 547–553.
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2017-08-01
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บทความวิจัยจากการประชุมวิชาการระดับชาติ"วิทยาศาสตร์วิจัย"ครั้งที่ 9
