The common understanding of a diamond is that it is virtually indestructible, the hardest substance found in nature. The definitive answer is that a diamond can indeed be split or broken with a forceful blow, revealing a surprising vulnerability in the world’s most famous gemstone.
Hardness Versus Toughness: The Answer
The ability of a diamond to be broken comes down to a distinction between two separate physical properties: hardness and toughness. Hardness refers to a material’s resistance to scratching or abrasion, which is measured on the Mohs scale. Diamonds sit at the very top of this scale with a rating of 10, meaning only another diamond can scratch it. Toughness, however, is a material’s resistance to breaking, chipping, or fracturing when subjected to impact or force. While diamonds are exceptionally hard, their toughness rating is only considered fair to good, making them relatively brittle. For example, some materials, like jade, are far less hard than a diamond but possess an “exceptional” toughness rating, making them much less likely to shatter upon impact.
The Role of Crystal Structure and Cleavage
The diamond’s weakness to impact is directly related to its atomic structure. A diamond is composed of carbon atoms arranged in a rigid, repeating tetrahedral lattice, with each atom connected to four others by extremely strong covalent bonds. This three-dimensional network of bonds gives the diamond its unparalleled resistance to scratching and its overall strength.
Despite the strength of these bonds, the crystal structure contains specific directions of weakness known as cleavage planes. These are planes within the diamond where the carbon atoms are slightly farther apart, causing the bonds between them to be less tightly held. When a diamond is struck parallel to one of these planes, the force does not need to overcome the entire network of bonds simultaneously. Instead, the energy is channeled along the plane of weakness, causing the diamond to split cleanly and smoothly.
How Diamonds Are Actually Shaped and Split
The structural vulnerability of the cleavage planes is not just a point of weakness but is also deliberately exploited by professionals to shape raw diamonds. One method is called cleaving, where a diamond cutter places a steel blade into a prepared groove and strikes it to split the stone along its natural cleavage plane. When a cleavage plane is not present where a cut is desired, other methods must be used to shape the material. Sawing uses a diamond-coated blade or a high-powered laser to cut through the stone in directions where the atomic bonds are strongest. The final process, polishing, involves grinding the diamond’s surface against a spinning wheel coated with diamond dust, using the material’s own hardness to create the mirror-like facets.