Why do carbon-carbon bonds in diamond compress very little under pressure?

Carbon-carbon bonds in diamond compress very little under pressure primarily because of their high bond strength. In the crystal structure of diamond, each carbon atom is covalently bonded to four other carbon atoms in a dense, three-dimensional tetrahedral network.12

The magnitude of bond compression—the shortening of interatomic distances—is directly related to the strength of the chemical bonds involved. Because these covalent bonds are exceptionally strong, they exhibit minimal compression, measured at roughly 0.07 percent per GPa. Unlike materials that contain weaker bonds or those that can compress significantly through the bending of bond angles between polyhedrons, the rigid, close-knit framework of diamond lacks the structural flexibility to undergo substantial volume reduction under pressure.3