🔷 Sapphire Optics Lab: Refractive Index 1.762-1.770, Dispersion and Brilliance of a Cut Sapphire

Sapphire (Al2O3 with Fe2+/Ti4+ (blue)): refractive index 1.762-1.770, Mohs hardness 9, dispersion 0.018. Sapphire is gem-quality corundum of any colour except red, and the classic blue comes from iron and titanium sharing electrons across neighbouring sites in the crystal. It shares ruby's hardness of 9 and refractive index near 1.76, so well-cut stones stay bright and durable.