Ceramic materials like glass have high bulk modulus and hardness. The forces at the tip of a crack are much higher in these high-hardness materials so despite b

Ceramic materials like glass have high bulk modulus and hardness. The forces at the tip of a crack are much higher in these high-hardness materials so despite being harder to bend they have poor toughness [1]. That is cracks propagate much more easily. The likelihood of your glass breaking when you drop it is almost entirely governed by the small scratches existing before you drop it - if they are bigger then there will be more stress concentrated and one or more will propagate catastrophically across the glass. New glass is substantially tougher than old glass. In comparison, metals can absorb the energy in cracks through several mechanisms ranging from the movement and formation of defects in the atomic arrangement in the metal crystals to large scale plastic flow. [1] http://en.wikipedia.org/wiki/Fracture_toughness http://en.wikipedia.org/wiki/Fracture_toughness