Answer:
Since they are both made of carbon their chemical properties are the same.
Most physical properties of a solid like hardness, melting point, conductivity of heat/electricity, etc. largely depend on it's crystal structure.
Graphite and diamond have very different structures.
Graphite has a layered sheet-like structure with each layer consisting of hexagonal rings, this is because all carbon atoms are sp2 hybridised.
Diamond has a tetrahedral structure since all carbon atoms are sp3 hybridised.
Explanation:
