The Mi 13's rear lens cover isn't sapphire. According to the official information released by Xiaomi, the rear shell of the Mi 13 is made of ceramic, which uses ceramic technology and has the characteristics of high strength and wear resistance. Ceramic materials are more comfortable to use and can effectively prevent scratches and fingerprints. Sapphire is a transparent gemstone material with high hardness and good light transmission, widely used in fields such as watches and mobile phone camera lenses. Although sapphire back cover is common in mobile phone designs, this material is not used on the Mi 13. The Mi 13's ceramic back cover is designed to provide better touch and durability, while also displaying unique aesthetic and craftsmanship values.