Sapphire glass is much harder and more scratch resistant than mineral glass. This means that a watch with a sapphire crystal will be more durable and will retain its appearance for longer. Sapphire glass is also more shatter-resistant than mineral glass, so it's less likely to break if the watch is dropped or hit. Finally, sapphire glass has a higher refractive index than mineral glass, which means it can transmit more light and produce a brighter, more "lively" image.