Actually, sapphire is already more transparent than window glass and is 100% aluminum oxide. Aluminium oxynitride is a transparent ceramic that has similar properties to sapphire but is not quite as strong or as expensive.
I'm weird, but the nicest part of sapphire for me was that it meant i could keep my phone in the shop without worrying about the screen getting scratched from saw blades, chisels, or carbide marking knives i put in my pocket.
Of course, i guess i'd have the opposite problem of the phone scratching those things, but ...
