❤️ Ruby Optics Lab: Refractive Index 1.762-1.770, Dispersion and Brilliance of a Cut Ruby

Ruby (Al2O3 with Cr3+): refractive index 1.762-1.770, Mohs hardness 9, dispersion 0.018. Ruby is the red variety of the mineral corundum (aluminium oxide) coloured by a little chromium. Chromium ions absorb yellow-green and violet light and, at the same time, re-emit deep red light, which gives fine rubies their glow.