🟠 Topaz Optics Lab: Refractive Index 1.609-1.643 (typically 1.619-1.627), Dispersion and Brilliance of a Cut Topaz

Topaz (Al2SiO4(F,OH)2): refractive index 1.609-1.643 (typically 1.619-1.627), Mohs hardness 8, dispersion 0.014. Topaz is an aluminium fluorosilicate with Mohs hardness 8 and a refractive index of 1.62. It has a perfect cleavage in one direction, so it can split along the base if knocked even though it is hard.