Crystals
The crystal is the transparent protective covering fitted tightly over the face of the watch. Since it is exposed to all sorts of shocks and blows, the crystal should be as hard as possible. Softer materials will scratch and break easily, which will make the watch less attractive and possibly unreadable, or if shattered, can damage the watch beyond repair. The crystal is held in place by the bezel.
A crystal can be made from any clear material, from plastic to synthetic sapphire, which is the hardest and most expensive crystal available. The following information tells about most popular crystal types and their relative hardness.
Plastic Crystal - Does not resist scratches.
Mineral Crystal - Hardened glass that resist some scratches.
Synthetic Sapphire Crystal - Hardened glass with a sapphire coating to help resist scratches.
Sapphire Crystal - Scratch resistant, very hard.
