A diamond is a crystalline form of pure carbon, famous for its exceptional physical properties. This reputation has led to the common but inaccurate perception that diamonds are indestructible. While diamonds are the hardest natural material known, this popular belief fundamentally misunderstands the science of material strength. The atomic structure makes diamonds incredibly resistant to one type of damage, yet surprisingly vulnerable to others. Understanding how a diamond can be broken requires examining the distinct concepts of hardness, toughness, and chemical stability.
Understanding Hardness and Toughness
The confusion surrounding a diamond’s durability stems from conflating two material science terms: hardness and toughness. Hardness refers exclusively to a material’s resistance to being scratched or permanently deformed. A diamond’s carbon atoms are arranged in a dense, three-dimensional tetrahedral lattice, giving it the highest rating on the Mohs scale of mineral hardness. This unparalleled scratch resistance makes it the ideal material for industrial cutting and polishing applications.
Hardness does not equate to toughness, which describes a material’s ability to absorb energy before fracturing. Toughness is the resistance to breaking, chipping, or cracking under impact or high stress. Although diamonds are the hardest natural substance, they possess surprisingly low to moderate toughness compared to common engineering materials like specialized ceramics or steel alloys.
This mechanical profile means that a diamond is highly resistant to surface wear but is also brittle. A material that is hard yet brittle will not deform plastically when struck; instead, it immediately transfers the energy through its structure. If the kinetic energy from an impact exceeds the stone’s limit, the material will fail suddenly by fracturing, rather than bending or denting. This distinction is the fundamental reason why a diamond can be broken despite its legendary reputation.
Physical Ways Diamonds Can Be Damaged
A diamond’s specific vulnerability to impact is a direct result of its internal crystalline structure and the existence of cleavage planes. While the carbon atoms are strongly bonded, the structure is not perfectly uniform in its resistance to all types of force. Cleavage planes are inherent, flat planes of weakness within the crystal lattice where the atomic bonds are slightly weaker.
A diamond possesses four sets of perfect cleavage planes, oriented parallel to the faces of an octahedron. If a sharp, concussive force is applied precisely parallel to one of these planes, the energy propagates along the path of least resistance. This targeted impact can cause the diamond to split cleanly or fracture. This is the exact technique diamond cutters utilize to shape rough stones with minimal material loss.
The existence of these planes means that the diamond’s legendary hardness is irrelevant when force is delivered in the wrong direction. A stone can resist being scratched by anything, but a sharp blow from a hammer or a fall onto a hard surface at the right angle can result in a catastrophic fracture. This mechanical failure highlights the difference between resisting surface abrasion and resisting internal structural separation.
Chemical and Thermal Alteration
Beyond physical damage, a diamond can be destroyed by both thermal and chemical processes, revealing its fundamental instability outside of its geological formation environment. The most surprising vulnerability is its susceptibility to heat and fire. Since a diamond is pure carbon, it will oxidize, or burn, when exposed to oxygen at high temperatures.
In the presence of air, the diamond’s ignition point is between \(700^\circ\text{C}\) and \(900^\circ\text{C}\) (\(1,292^\circ\text{F}\) to \(1,652^\circ\text{F}\)). When this threshold is reached, the carbon atoms react with oxygen to form carbon dioxide gas. This reaction causes the diamond to slowly disappear. This chemical combustion demonstrates that despite its reputation, a diamond is entirely combustible.
A different type of thermal destruction, known as graphitization, occurs when a diamond is heated in the absence of oxygen, such as in a vacuum or inert gas. At standard atmospheric pressure, the diamond structure is metastable, meaning it is not the most stable form of carbon. When heated to approximately \(1,700^\circ\text{C}\) (\(3,092^\circ\text{F}\)) or higher, the diamond structure begins to revert to its more stable form: graphite.
The carbon atoms rearrange from the dense tetrahedral lattice into the layered sheets of graphite, causing the crystal to blacken and degrade. Diamonds are also chemically vulnerable to certain molten metals. When submerged in liquid metals like iron, cobalt, or nickel, the carbon atoms dissolve into the melt. These molten metals act as a solvent, absorbing and dispersing the carbon atoms from the diamond structure.