Answer
See work below for details.
Work Step by Step
Graphite’s structure consists of flat sheets of carbon atoms bonded together as interconnected hexagonal rings.
Although the covalent bonds within the sheets are strong, the interactions between the sheets are weak, allowing the layers of graphite to slip easily past each other and making graphite a good lubricant. However, diamond is not a good lubricant, because it is an extremely strong network covalent solid, where all of the carbon atoms are covalently bonded.
