Color Improvement Study in Brazilian Elbaite Tourmalines via Heat Treatment

Abstract

Brazilian tourmalines come in a variety of colors and hues, with the majority originating from northern Minas Gerais state. These gemstone minerals have significant commercial value and can undergo color changes when exposed to appropriate heat treatment. The tourmaline group is large and includes a wide range of colors and hues, the most prized being green, blue, and red. Previous studies have shown that heat treatment of this group of minerals is possible to improve their color. Elbaite tourmalines are found in pegmatites, most commonly found in northern Minas Gerais state, in the Araçuaí and Coronel Murta regions. The color of this group of tourmalines is due to chemical elements introduced as impurities, and these impurities give it various hues. This study evaluated the color and hue changes of several Elbaite tourmalines, particularly the green and blue ones. As for the other colors, such as pinks, grays, and multicolors, they became very light to completely colorless. Black elbaite tourmalines remained stable in all temperature ranges.