Uvarovite Garnet Chemical composition Ca 3 Cr 2 (SiO 4 ) 3 alcium chromium silicate Crystal system Cubic Habit Dodecahedra Cleavage Hardness Optic nature Isotropic Refractive index 1.86-1.87 Birefring...Uvarovite Garnet Chemical composition Ca 3 Cr 2 (SiO 4 ) 3 alcium chromium silicate Crystal system Cubic Habit Dodecahedra Cleavage Hardness Optic nature Isotropic Refractive index 1.86-1.87 Birefringence None Specific gravity 3.77 Lustre Vitreous Figure \PageIndex1: Uvarovite Photo courtesy of Rick Martin Uvarovite is hardly ever found in crystals large enough to be cut into gemstones.