This is a interesting topic. it decides the quality of watch in normal quality or premium quality. Actually Each watch part has several options for material to make the different quality. for example, the watch case, it would be in Alloy material for price usd8-10/pc, or Stainless steel in usd18-30/pc, or Titanium material for higher price or Carbon fiber material in even more high price. Price always connects to quality. what price, what goods. in this case, we compare the quality of Mineral watch glass and Sapphire crystal watch parts.
Firstly, we all know the sapphire crystal can't be scratched except the real diamond. as it is one of hardest materials in the world. pls see below video. it is very obvious to see the different. I also tested the Hardened Mineral watch glass as well. it is in the middle level, not so easy to be scratched as mineral glass.
Secondly, Water drop test, it is a very funny test too. pls see below photo. the sapphire crystal seems have something to hold the water in round shape. water spread immed even it is flat.
Thirdly, the Color, but it can't be all right as some mineral glass with white color as Sapphhire too. you can see from above photo, mineral glass are a bit greenish from side.
Fourthly, the feeling, if you touch the glass, sapphire would be cooler than mineral watch glass.
Generally, the good quality watches or Mechanical automatic watches are in Sapphire watch glass.