According to a popular advertising slogan, released in 1948, diamonds are forever. However, using an adequate amount of heat and sufficient oxygen, a diamond could turn into smoke. In fact, diamonds are carbon (just like coal), so it takes more energy to burn them. Thus, although a large amount of energy is needed to overcome the intramolecular forces of carbon, eventually the diamond would burn.
According to Rick Sachleben, a chemist at the American Chemical Society, carbon must first be converted into a gaseous form so that it can react with air and form a flame. And to do this, the best way is to apply an enormous amount of heat, since diamonds begin to burn around 900 degrees Celsius.
When a diamond is first burned, it begins to glow red and then turns white. The heat develops a reaction between the surface of the diamond and the air, turning the carbon into a colorless gas (i.e. carbon monoxide). Carbon monoxide, in turn, generates more heat and reacts with oxygen.
However, the fire does not usually last very long, since to feed the flame you would need pure oxygen instead of ambient air, which only contains 22% oxygen. In addition, the carbon monoxide that rises from the diamond ignites in the presence of oxygen, creating a fire that appears to glide over the surface of the stone.
They can be damaged by flames
According to the Gemological Institute of America (GIA) diamonds could be damaged by the flames of a fire, even without pure oxygen. Thus, a diamond caught in a house fire will not turn to smoke or ash, but will burn enough to appear white. However, if the burnt parts of the diamond were cut, a much smaller stone would be seen, but also lighter.
On the other hand, when carbon is burned into pure oxygen, it produces carbon dioxide and water. Therefore, a pure carbon diamond could theoretically disappear completely if burned long enough. However, most diamonds have some impurities, such as nitrogen, so the reaction is highly unlikely to be that simple.
