Twinned chrysoberyl crystal (30 x 50 mm), Santa Tereza, Espírito Santo. Specimen from the Luiz Paixão Collection belonging to the set of exhibits of the Museu de Geociências of the Universidade de São Paulo. Photograph taken by Marcelo Lerner. Chrysoberyl is an aluminum and beryllium oxide that occurs in tabular or prismatic crystals, with frequent macle of hexagonal habit and “V”-shaped twinning, which are valued highly by collectors. Its varieties produce several gems, such as the “chrysolite” or golden yellow chrysoberyl; the alexandrite, whose color ranges from green to red depending on whether the light is natural or from an incandescent light bulb, and “cymophane”, which presents a characteristic optical effect called “cat’s eye”.