Chemical formula BeAl2O4:Cr3+ Density, g / cm3 3,69-3,75 Mohs Hardness 8,5 Syngony Rhombic Options of el.cells a=4.248, b=9.41, c=5.481 Refractive index 1,745-1,754 Birefringence 0,01 Pleochroism Strong Color at daylight Greenish Blue Color at incandescent bulbs Violet-purple