🟣 Amethyst Optics Lab: Refractive Index 1.544-1.553, Dispersion and Brilliance of a Cut Amethyst

Amethyst (SiO2 with Fe (colour centres)): refractive index 1.544-1.553, Mohs hardness 7, dispersion 0.013. Amethyst is purple quartz, silicon dioxide coloured by iron that has been changed by natural radiation. It has a Mohs hardness of 7 and a refractive index of about 1.55, so it is durable enough for everyday jewellery but shows modest sparkle.