Sapphire is a gem known as being precious belongs to the Corundums’ family. Sapphire exists in almost all colors but without precision of these ones, it refers to the blue color’ stones. There are many hues, but the « royal blue » is highly prized. It’s hardness is 9 on the Mohs scale. The heating treatment is very common. Without treatment, the sapphire is rare and its value is higher. Chemical composition Al2O3.