Effect of Heat Treatment on Madagascar Dravite Tourmaline: UV-Visible and Diffuse Reflectance Infrared Spectroscopic Characterization

The color change and chemical behavior of Madagascar dravite when subjected to heating in air atmosphere were studied by energy-dispersive X-ray fluorescence spectrometry, UV-visible (UV-vis) spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Heat treatment was performed with temperatures of 500, 600, and 700A degrees C for 2 h. Colors and color differences were measured and evaluated using CIELAB color measurement. The origin of color and its change after treatment are assessed via UV-vis spectra. The diffuse reflectance infrared spectra of the dravites revealed major absorption bands of OH, BO3, Si6O18, and R-OH (where R = Fe, Mg). The variation of infrared spectra with increasing temperature indicates the deformation of R-OH bonds in an octahedron and, further, the deformation of BO3 and Si6O18. The results of color change may be utilized to enhance the color or clarity in dravite tourmaline and for generating satisfactory color.