Diamond to Coal
Name: Priscilla J.
My question is about how hot a fire must be to turn a diamond into coal. The reason I
ask is my house burned down. In the rubble we found my deceased Mother's wedding ring. It had
three diamonds in it. After the fire I took the ring to a jewelry store and asked to have the
ring cleaned. The person there told us the diamonds had all turned to coal. In the place where
the diamonds once were are bright black shiny stones. The jewelry person said it was unusual.
Just how hot does a fire have to be to change a diamond into coal? Why did not the gold band part
melt? I am just curious. I am happy to have the ring even if it is now coal. I just did not know a
diamond could turn to coal. Can you please provide me with some info on this?
Something is amiss in the circumstance you describe. Diamonds do not revert to coal in a sufficiently
hot fire -- they simply burn up and form carbon dioxide gas leaving no ash of any kind. In the
absence of oxygen, a diamond will sublime -- evaporate.
You mentioned that the gold band did not melt. This is further evidence that the fire was not hot
enough to actually burn the diamonds. Ordinarily, diamond jewelry in precious metal settings burn to
leave nothing behind but the melted metal.
I do not know what the jeweler had in mind with the "turned to coal" comment. If the ring really had
diamonds in it, I suspect they were simply dirty with soot from the fire. If the diamonds were
actually "turned to coal" the remaining stones would be easy to crush. Unlike coal, diamonds are
I have not heard of this phenomenon, but a jeweler can readily test for diamonds with a special
instrument. He/she is probably correct that you no longer have diamonds. It is not possible to
turn diamonds into coal--coal is formed in a different way. Diamonds are metastable (they are not
stable at our pressures and temperatures at the surface of the earth), and may slowly
turn to graphite anyway. If the jeweler is correct that the diamonds have converted, I suspect the
heat from the fire may have caused the collapse of the crystal structure. Pure gold melts at around
2000F. I do not know typical house fire temperatures, but assuming 1000F-1200F, I think it may be
possible to affect the diamond lattice without melting the gold. I answered a question before about
diamonds--you may search Ask A Scientist (by topic or by my name, I believe) if you want to know
more. I know there is a web site in that answer where you can find a diagram showing the different
forms of carbon at different temperatures and pressures. I am sure you will treasure your mother's
ring just as much. Please accept my sympathies for the ring and for the loss of your other
Click here to return to the Chemistry Archives
Update: June 2012