Diamonds are widely celebrated for their permanence, leading to the common belief that they are indestructible. While a diamond is indeed the hardest natural substance known, this superlative only refers to a specific type of material strength. The perception that a diamond is unbreakable is a pervasive myth, as these gemstones are quite susceptible to shattering and fracturing under certain conditions. Understanding the difference between a material’s resistance to scratching and its resistance to impact explains why this famously tough mineral can still be broken. The physical structure of a diamond dictates its impressive resistance to abrasion, yet it also contains specific points of weakness.
Defining Diamond Hardness
Hardness in material science refers specifically to a substance’s resistance to being scratched or abraded by another material. This property makes diamonds valuable for industrial applications, such as cutting, drilling, and grinding other hard materials. The Mohs scale of mineral hardness ranks minerals from 1 to 10 based on this scratch resistance, with diamond occupying the top position at 10. This extraordinary hardness is a result of the diamond’s internal crystalline structure. Each carbon atom is tightly bonded to four neighbors in a dense, repeating tetrahedral lattice, forming an incredibly strong and rigid network.
The Structural Weakness of Cleavage
A material’s hardness is distinct from its toughness, which is its resistance to breaking, fracturing, or shattering upon impact. While diamonds excel in hardness, they possess only moderate toughness, making them brittle due to the orderly crystalline structure. The tetrahedral arrangement creates distinct internal planes where the atomic bonds are slightly weaker than in other directions. These are known as cleavage planes, and diamonds possess four sets of these planes. A sharp, focused blow delivered precisely parallel to one of these cleavage planes will cause the diamond to split cleanly and smoothly, a vulnerability historically utilized by diamond cutters to separate a rough stone.
Real-World Damage Scenarios
The brittleness caused by cleavage planes translates into practical risks for diamonds in jewelry and industrial settings. A common way a diamond can be damaged is through a direct, sharp impact, such as accidentally striking a diamond engagement ring against a hard surface. If the impact force is directed along a cleavage plane, the stone can chip or split, a risk that is higher for cuts with pointed tips, like the princess or pear shape. Diamonds can also be damaged by thermal shock, which involves a rapid, extreme change in temperature. Quickly moving it from a hot environment to a cold one causes the outer layer and the interior to expand or contract at different rates, creating intense internal stress that leads to fractures and visible cracking.