Jan Murray age 9 of  Idaho for her question:

Does fire damage diamonds?

Diamond is the hardest substance in the world, It is also just about the most precious, You might suppose that such a tough material could withstand the heat' of a fire. Not at all. In a hot fire, a hard, precious diamond is far worse off than an ordinary pebble from the beach, It will catch on fire and burn away like a piece of glowing coal. If the fire reaches a heat of 3500 degrees Centigrade, the diamond will burn away to nothing.

Precious diamond is made of pure carbon. Graphite is also made of pure carbon. The only difference is in the arrangement of the carbon atoms in the two substances. Graphite, the lead in a pencil, is the last stage of coal making. Coal is also made mostly of carbon. So is petroleum, These substances burn so well that we use them as fuels.

If diamonds were as plentiful as coal and petroleum, maybe we would use them for fuel. Imagine heaping a fresh shovelful of diamonds into the grate to keep the fire goings.