Rubellite Tourmaline Hardness: 7.5 Optic nature: Uniaxial - Refractive index: 1.62 - 1.64 Birefringence: 0.014 - 0.022 Dispersion: Low, 0.018 Specific gravity: 3.06 Lustre: Vitreous Pleochroism: Weak to strong