What causes the difference in hardness between diamond and graphite?

The difference in hardness between diamond and graphite is primarily due to the way their atoms fit together, which is a reflection of their distinct structures. In a diamond, carbon atoms are arranged in a three-dimensional tetrahedral lattice structure. Each carbon atom is bonded to four other carbon atoms through strong covalent bonds, which create a robust and rigid framework. This extensive bonding network is what contributes to diamond’s exceptional hardness.

In contrast, graphite has a planar structure where carbon atoms are bonded in sheets of hexagonal arrangements. Within each sheet, the carbon atoms are bonded strongly, but the sheets themselves are held together by weaker van der Waals forces, allowing them to slide over one another easily. This layering is what gives graphite its lubricating properties and makes it much softer compared to diamond.

The other options, while related to general properties of materials, do not specifically address the crucial structural differences that account for the hardness disparity between diamond and graphite.