I. M. Gei posted:

Fun Fact: Contrary to popular belief, diamonds are NOT forever. Their Moh's hardness is only a measure of their SCRATCH resistance; they are surprisingly fragile against impact resistance and even a light tap with a hammer will shatter one into a million pieces.

Additionally, diamonds actually WILL burn up in a fire...... sort of! That's because from the instant they are mined, and are thus no longer held together by the intense pressure of the earth's crust, diamonds undergo a slow but constant state of degradation into graphite dust. Normally this process happens too slowly for our eyes to see, taking hundreds if not thousands of years to become noticeable under normal conditions, but the rate of decay is proportional to the surrounding temperature, and if the temperature rises to a high enough point — like in a fire, for example — then the breakdown will occur in only a few minutes or even a few seconds!

So, technically fire won't burn a diamond, but it will make it turn into worthless dust a whole lot faster than it would otherwise.