Sapphire is one of the gemstones and can be called as transparent crystal. It is regularly used in jewellery such as rings, earrings, or crowns. A pure sapphire is very hard to obtain, to overcome this issue, synthetic sapphire is the solution. In general, synthetic sapphire is manufactured by heating with high temperature and high pressureuntil it turns into aluminium oxide powder (sapphire is, after all, just a compound of aluminium and oxygen). Synthetic sapphire is referred to as sapphire glass.
The sapphire glass is highly transparent, so definitely it won't affect the clarity of the screen. Sapphire glass is very very durable, it is more of the hardness of the normal screen. It scores lvl 8-9 in Mohs scale which is close to the hardness of diamond. Impressive. Not everything is perfect, sapphire glass shatters more easily than other types of glasses.