Sapphire is one of the hardest materials on the face of the earth, surpassed only by diamonds. Apple is rumored to be employing sapphire glass on some of its more expensive iPhone models this year. The reason for such a restriction is the cost of sapphire glass, which is said to be much more costly to use than Corning's Gorilla Glass.
Recently, Verizon launched the Kyocera Brigadier, which is the first smartphone in the U.S. to come with a sapphire glass display. The device "is virtually scratchproof and protects from a screen-first drop onto rocks, where tests show it less likely to break than strengthened touch-panel glass," according to both Verizon and Kyocera. Big Red is currently offering the phone for $49.99, with a signed two-year pact. Despite the use of sapphire glass, this happens to be a mid-range device with a 4.5 inch screen featuring a 720 x 1280 resolution, powered by a quad-core 1.4GHz Snapdragon 400.
Using sapphire glass for some of its displays would seem perfectly in character for Xiaomi, which is known as the "Apple" of China
Thanks for the tip!