Answer the following question:

The refractive index of diamond is much greater than that of ordinary glass. Is this fact of some use to a diamond cutter?

Yes,

The refractive index of diamond (2.42) is more than that of ordinary glass (1.5). The critical angle for diamond is less than that for glass. A diamond cutter uses a large angle of incidence to ensure that the light entering the diamond is totally reflected from its faces, so that the diamond sparkles.