Parti-Colored Tourmaline Classification
variations of two or more colors usually green, blue and red
appearance, refractive index and high birefringence; then optic figure, pleochroism and specific gravity
Not all parti-colored tourmaline is elbaite tourmaline Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH).Dark material might have a birefringence as high as 0.040.Pyroelectric: development of opposite charges at the ends of a tourmaline crystal due to change in temperature. Piezoelectric: development of opposite charges at the ends of a tourmaline crystal when placed under stress.