The hardness of sapphire is 9 (Mohs hardness). It is a general term for all gem-grade corundum except red, and its main component is aluminum oxide (Al2O3). Due to its high hardness and high refractive index, sapphire is a very important gemstone besides diamond, and is one of the five most precious gemstones in the world.
However, although sapphire is hard, it may contain internal cracks, so it is still necessary to avoid strong impact or falling to ensure its integrity.