The common idea of a diamond being an unbreakable object is largely a misconception, despite its status as the hardest natural material on Earth. Diamonds are composed of carbon atoms arranged in an extremely dense structure, which provides immense strength against abrasion. However, this impressive atomic arrangement does not guarantee the stone’s integrity against all forms of mechanical stress. Diamonds are susceptible to damage, chipping, and fracturing under the right conditions and force.
Hardness is Not Inductibility
The durability of any material is defined by three distinct properties: hardness, toughness, and stability. Hardness refers only to a material’s resistance to being scratched or abraded. Diamonds receive the highest possible rating, 10, on the Mohs scale of mineral hardness, meaning only another diamond can scratch its surface.
This exceptional hardness is frequently confused with toughness. Toughness measures a material’s ability to resist breaking, chipping, or fracturing when a sharp force is applied. It measures how effectively the material absorbs impact energy before failing. While diamonds are the hardest material, their toughness rating is only considered good to moderate.
This combination of extreme hardness and moderate toughness means a diamond is relatively brittle. A common analogy compares a diamond to a piece of glass, which is hard but shatters easily, while a piece of steel is softer but very tough because it bends instead of breaking. A diamond resists surface wear but can still be vulnerable to a sharp, sudden blow.
The Structural Weakness of Cleavage
The diamond’s breakability is explained by its internal crystalline structure. Carbon atoms are arranged in a tetrahedral lattice, covalently bonded to four neighbors, creating incredible density. This arrangement defines planes of perfect cleavage, which are specific directions where the atomic bonds are inherently weaker.
The most prominent weakness is the octahedral cleavage, corresponding to the {111} crystallographic planes. Along these planes, the distance between layers of carbon atoms is slightly greater, requiring less energy to break the bonds cleanly. A sharp impact delivered parallel to one of these four planes can cause the diamond to split easily.
This property is actually exploited by diamond cutters, who use a precise blow to cleave a rough stone along a cleavage plane to remove large sections before the final faceting process. For the diamond owner, this structural vulnerability means a direct hit at a specific angle can result in a clean, predictable fracture.
Practical Ways Diamonds Can Be Damaged
Diamond damage usually occurs when a vulnerable point of the stone is struck. The girdle (the thin edge separating the crown from the pavilion) and sharp points on certain cuts, such as the marquise or princess, are particularly susceptible to chipping. A direct impact against a hard surface like granite or metal can easily cause a fracture along the cleavage plane near these exposed areas.
The diamond’s structural integrity can also be compromised by internal characteristics known as inclusions. While most small inclusions do not affect durability, large fractures called “feathers” or exposed knots that reach the surface can create stress points. If a feather inclusion is located near the girdle, a subsequent impact can cause the crack to deepen and spread, potentially leading to a major break.
A less common but severe cause of damage is thermal shock, which involves rapid changes in temperature. Diamonds have high thermal conductivity, meaning they heat and cool very quickly, causing the lattice structure to expand and contract rapidly. Sudden exposure to extreme heat, such as from a torch or a house fire, can induce internal stress that leads to cracking or fracturing.