Andrzej_HaSapphire crystal coated. Not sapphire like the gem, but rather the crystal made in a lab/factory. They are used to to their high amount of hardness and clarity with little distortion. They are resistant to scratching. In this case it's sapphire coated, rather than pure sapphire crystal, so I would not call it as durable, but it's on you're wrist side, so I wouldn't worry.