Sapphire, with a Mohs rating of 9.0, right behind to diamond.
Three-layer coating process technique (Anti-Fingerprint Coating, Anti-Reflection Coating, High Transmittance Coating)
Remarkable Anti-pollution ability, High Transparency
Clearly readable even under the sun bright
Highly resistance to heat, corrosion and with Ultra-Cleanliness
Not only much more solid and more durable with superb-comfort, but also harmless to skin in use.