A diamond can be lit on fire, though not in the way one might typically envision a common material burning. This phenomenon occurs under specific, extreme conditions that involve intense heat and the presence of oxygen. Understanding the science behind this reaction reveals that it is not combustion in the traditional sense, but rather a chemical process known as oxidation.
What a Diamond Is
A diamond consists almost entirely of pure carbon atoms, typically around 99.95% carbon. These carbon atoms are arranged in a highly stable and rigid three-dimensional crystal structure known as the diamond cubic lattice. This unique atomic arrangement, characterized by strong covalent bonds, makes diamond the hardest known natural substance on Earth. While carbon is an element found in many forms that burn easily, such as coal or graphite, the diamond’s specific crystalline structure accounts for its exceptional stability.
Diamond Behavior Under Heat
Diamonds exhibit remarkable stability even when exposed to elevated temperatures. However, this stability is not limitless. When a diamond is heated in the presence of air, changes begin to occur at temperatures exceeding approximately 700°C (1,292°F). At these temperatures, the diamond’s surface can start to oxidize, which may lead to a blackening or clouding effect.
The Oxidation Process
The process often described as “lighting a diamond on fire” is actually an oxidation reaction. At very high temperatures, generally between 800°C and 1000°C (1,472°F to 1,832°F) in air, or even lower, around 690°C to 840°C (1,274°F to 1,540°F) in pure oxygen, the carbon atoms within the diamond react with oxygen. This chemical reaction forms carbon dioxide gas (CO2).
Unlike the burning of wood or other materials that leave behind ash, a pure diamond, when fully oxidized, essentially dissipates into a gas, leaving no solid residue. This complete conversion to carbon dioxide highlights the diamond’s pure carbon composition. The intensity of this reaction can vary, with smaller diamond crystals tending to burn more readily.
Real-World Scenarios
It is exceptionally difficult to cause a diamond to oxidize under typical household conditions. Despite popular misconceptions, diamonds are generally safe from accidental combustion. While household fires can reach temperatures of 1,000°F to 2,000°F (538°C to 1,093°C), these temperatures are often not sustained at the specific ignition point required for a diamond to fully oxidize.
Prolonged exposure to intense heat, such as that experienced in a house fire or from a jeweler’s torch, can still damage a diamond. This damage usually manifests as a cloudy or frosted appearance on the surface, which is a result of partial oxidation. In many cases, this surface damage can be removed by re-polishing the diamond, though it might result in a slight reduction in the stone’s size.