🍷 Garnet Optics Lab: Refractive Index Almandine 1.76-1.83; group range 1.714-1.888, Dispersion and Brilliance of a Cut Garnet

Garnet (X3Y2(SiO4)3 (e.g. almandine Fe3Al2(SiO4)3)): refractive index Almandine 1.76-1.83; group range 1.714-1.888, Mohs hardness 6.5-7.5, dispersion 0.024. Garnet is not one mineral but a group of silicates with the same cubic structure and different metal ions, which gives a range of colours and refractive indices from about 1.72 to 1.89. The deep red almandine and pyrope garnets of traditional jewellery have a refractive index near 1.76 to 1.80, hardness 7 and a dispersion higher than that of ruby.