Comment by symptic

It's worth mentioning that there is a difference between "hardness" and "toughness" when dealing with glass and gems/minerals. Hardness is the material's resistance against scratching, while toughness is its resistance to breakage. The iPhone uses a synthetic sapphire I believe (much like in many eyeglasses made today) which has a hardness of 9 on the Mohs scale (Diamond is 10), so it is very resistant to scratches, since only materials with a hardness the same or above can scratch it; that doesn't correlate with it's resistance to breakage. Many very hard materials are also very brittle and will crack or shatter more easily than anticipated.