Tourmalines have a very complex chemical composition, and more than a dozen mineral species are recognized within this group. Their highly variable chemical composition gives rise to a wide range of colors. Among the many varieties of elbaite tourmaline are verdelite (green), indicolite (blue) and rubellite (red). Some tourmaline specimens display multiple colors. Optical effects include pleochroism (a change of color when the gemstone is rotated) and chatoyancy (a “cat’s-eye” seen in reflected light).