Which of the following is/are true about diamond?
It is very hard.
It is very brittle.
Diamond is a very hard material, i.e., it offers a lot of resistance when subjected to deformation. In spite of being hard, it is brittle. Hardness should not be confused with brittleness. Hardness is a measure of how difficult it is to deform something, while, Brittleness is a measure of how easily something breaks apart under pressure.
Also, Diamond is not malleable or ductile, i.e., It doesn't get shaped into wires or drawn into sheets when pressure is applied to them.