Diamond and graphite show different physical properties although they are made up of carbon and show the same chemical properties. What is this property called?

Hint: Diamond and graphite are the naturally existing allotropic form of the element carbon having the same composition but different arrangements of atoms.

Complete step-by-step answer:
The other name of graphite is black lead or plumbago. The structure of graphite represents a layer of six carbon atoms attached to the other three carbon atom arranged in a hexagonal form and linked to each other by a covalent bond. Due to the weak forces between the atoms, the layer can slip with each other. The carbon atom has one electron free which makes them a good conductor.
Diamond is the purest allotrope of carbon where one carbon is attached to four other carbon atoms and in a tetrahedral fashion. This continuous arrangement leads to a three-dimensional structure of diamond. Diamond is also the hardest allotrope as the carbon atoms are bonded together with a very strong covalent bond.
 Both are the allotropes of carbon, but they differ in the chemical properties due to their different arrangement of carbon atoms.
The property by which the element exists in more than one physical form but differs in the structure is known as allotropy or allotropism.

Therefore, the property by which diamond and graphite show different physical properties although they are made up of carbon and show the same chemical properties is allotropy.

Note: Fullerene is another allotrope of carbon where carbon atoms are connected with each other by a single and double bond which results in a cage ring like structure.