The diamond is widely regarded as the ultimate symbol of strength and permanence, often cited as the hardest naturally occurring material. This perception leads to the common question of whether this seemingly indestructible substance can be crushed by mechanical force. The answer requires a scientific understanding of material properties. Examining the question reveals that the diamond’s reputation for strength is based on its atomic structure, but its performance under stress depends on the specific type of force applied. The true measure of its resistance is found in the science of how materials resist compression, fracture, and phase change.
The Atomic Architecture of Diamond
The diamond’s exceptional strength begins at the atomic level, where carbon atoms are linked in a precise and stable arrangement. Each carbon atom forms four strong covalent bonds with its neighboring carbon atoms. These bonds share electrons, creating the strongest type of chemical bond found in nature.
This bonding structure results in a three-dimensional lattice known as the diamond cubic crystal structure. The carbon atoms are organized into a rigid, repeating tetrahedral network that extends throughout the entire crystal. This continuous, interlocking framework provides the material with its immense structural rigidity and density.
The structure means that the entire diamond functions essentially as one giant molecule. A large amount of energy is required to deform this crystal, which is the foundational reason behind the material’s properties. This perfect and dense packing of atoms is directly responsible for the strength that makes diamond the hardest known natural substance.
Hardness, Toughness, and Compressive Strength
To understand if a diamond can be crushed, it is necessary to distinguish between three distinct measures of material strength. Hardness refers to a material’s resistance to scratching or abrasion, which is the property for which diamond is most famous, scoring 10 on the Mohs scale. However, a material can be extremely hard without being shatterproof.
Toughness, or fracture resistance, measures a material’s ability to absorb energy before fracturing or shattering upon impact. Diamonds have a toughness rating that is considered good, but it is not infinite, especially when compared to many engineering alloys. A diamond can fracture if struck sharply, demonstrating that toughness is a different metric than its celebrated hardness.
The property most relevant to the question of crushing is compressive strength, which is a material’s resistance to being uniformly squeezed or compressed. Diamond exhibits an exceptionally high compressive yield strength, typically measured between 130 and 140 GigaPascals (GPa). For comparison, one GigaPascal is roughly 145,000 pounds per square inch.
This extreme compressive strength means that uniform crushing requires specialized equipment capable of generating hundreds of thousands of times the pressure found at sea level. Scientists rely on this property when building high-pressure devices called diamond anvil cells, which use diamond to withstand pressures exceeding 600 GPa in laboratory experiments. Theoretical calculations suggest that the ideal compressive strength of a perfect diamond crystal could be even higher, potentially reaching over 470 GPa along specific axes.
The Physics of Failure
Despite its immense compressive strength, a diamond is not indestructible, and its failure under mechanical stress typically exploits a structural weakness called cleavage. Cleavage refers to the tendency of a crystal to split along specific planes of weakness due to the slightly looser atomic bonding along those directions. Diamonds possess four perfect cleavage planes, which are directions along which the crystal can be split relatively cleanly.
Diamond cutters, or cleavers, historically exploited these planes by striking a diamond precisely in the right spot to split the stone. This method is very different from true crushing, as it involves a targeted blow that separates the atoms along their weakest structural path. An impact that is not uniform and is directed along one of these cleavage planes can cause the material to fracture or chip.
True crushing, which means the uniform compression of the bulk material, requires overcoming the diamond’s full compressive strength across the entire volume. This level of force is virtually impossible to generate outside of a specialized laboratory setting or a geological event. Everyday forces, such as being hit with a hammer, are more likely to cause a fracture along a cleavage plane than to uniformly crush the entire crystal.
Beyond Crushing: Extreme Conditions
When a diamond is subjected to pressure far exceeding its fracture point, the material can undergo a phase transformation. This occurs under extreme conditions that push the material to its physical limits. Scientists use high-pressure, high-temperature (HPHT) techniques to study these transformations, sometimes resulting in the creation of synthetic diamonds.
One result of subjecting carbon materials to immense pressure, particularly from shock compression events like meteorite impacts, is the formation of Lonsdaleite. Lonsdaleite is a hexagonal form of diamond that is predicted to be even harder than the standard cubic diamond structure. This hexagonal structure forms under the intense, rapid pressures encountered during cosmic impacts, where the carbon atoms rearrange but retain some characteristics of the original graphite structure.
At even more theoretical extremes, such as pressures exceeding one terapascals (1 TPa), which is 10 million atmospheres, diamond is predicted to melt. Under these conditions, the carbon lattice collapses into a metallic fluid. These phase changes illustrate that the material’s structural integrity can be overcome by a complete atomic reordering under the most extreme conditions.