The quality of metal that describes its likliness for the crystals to become detached, becoming a crack. Metal is said to be 'brittle' if it is likely to crack--this can be reduced by
annealing the metal, allowing the crystals to realign. By their composition, some metals are more brittle than others: higher carbon steels are more brittle than lower carbon
steels , though they are also harder, and
brass is more brittle than
bronze . Note that
hardness and brittleness are distinct qualities, hardness referring to the metal's restistance to deforming and brittleness the tendency to crack.