Sapphire glass is a very hard material valued for its high endurance and scratch-resistance.
Durability for years to come
With a rating of 9 out of 10 on the Mohs scale, the sapphire crystal ranks high on the list of the hardest materials known to humans. For that reason, there are not many things that are able scratch it. These would include diamonds and some other especially hard types of rocks. Thanks to its durability, sapphire glass can look as good as new even on a watch that has been worn for many years.
Mineral glass that is more commonly used in watches is a much softer material, meaning it's a lot less durable and easier to scratch. That makes sapphire glass the better choice for quality watches that are designed to last.