Corundum is a mineral from the category of oxides and hydroxides and is the most frequently used industrial mineral worldwide. It also occurs naturally as a gemstone (sapphire, emerald, ruby). Chemically corundum is aluminium oxide with the chemical formula Al2O3.
What is the refractive index of white fused alumina compared with that of glass?
The refractive index of fused alumina is approx. 1.76, whereas that of normal glass types is approx. 1.4. The closer the refractive indices are to each other, the more transparent the system (e.g. varnishes).