What is the sapphire crystal?

Sapphire crystal is an optically transparent, crystalline material that belongs to the Rhombohedral, class 3m, crystallographic system. Some unique qualities of sapphire:

• Second only to diamond in hardness.
• Sapphire is thermally stable at extremely high temperatures with a melting point of 2030C.
• Exceptional chemical stability.
• Very low dielectric constant and very low loss tangent value.