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Can diamonds burn?

If diamonds can burn, are they really "forever"?
If diamonds can burn, are they really "forever"?
(Image: © Shutterstock)

Diamonds are forever, or so the slogan goes. But with the proper application of heat and enough oxygen, a diamond can go up in smoke.

Diamonds are carbon, just like coal. It takes a bit more to get them burning and keep them burning than coal, but they will burn, as numerous YouTube demonstrations will attest. The trick is to create the right conditions so that a solid diamond can react with the oxygen required to fuel a fire.

"You have to convert that solid [carbon] into a gas form, so it can react with the air to make a flame," said Rick Sachleben, a retired chemist and member of the American Chemical Society.

Related: Which is rarer: Gold or diamonds?

The best way to do that? Heat — and lots of it. In room temperature air, diamonds ignite at around 1,652 degrees Fahrenheit (900 degrees Celsius), according to West Texas A&M University physicist Christopher Baird. For comparison, a high-volatile coal (coal containing a relatively high amount of easily released gases) ignites at about 1,233 F (667 C), whereas wood ignites at 572 F (300 C) or less, depending on the type.

When first heated, a diamond will glow red, then white. The heat enables a reaction between the surface of the diamond and the air, converting the carbon to the colorless and odorless gas carbon monoxide (a carbon atom plus an oxygen atom).

"The carbon plus the oxygen to make carbon monoxide generates heat; the carbon monoxide reacting with the oxygen generates more heat; the rising heat causes the carbon monoxide to move away, so more oxygen is brought in," he told Live Science.

That fire, however, will amount to only a glow. Nurturing a flame on the surface of a diamond usually requires an extra boost: 100% oxygen rather than room air, which is only 22% oxygen. This increase in concentration gives the reaction all that it needs to self-perpetuate. The carbon monoxide rising from the diamond ignites in the presence of oxygen, creating a fire that seems to dance on the stone's surface.

"Almost everything burns incredibly in pure oxygen," Sachleben said.

Even without pure oxygen, diamonds can be damaged by flame, according to the Gemological Institute of America (GIA). Typically, a diamond caught in a house fire or by an overzealous jeweler's torch will not go up in smoke, but instead will combust on the surface enough to look cloudy and white. Cutting away the burnt portions will reveal a smaller, but once again crystal-clear, stone, according to the GIA.

When carbon burns in oxygen, that reaction produces carbon dioxide and water. A pure carbon diamond could thus theoretically vanish entirely if burned for long enough; however, most diamonds do have at least some impurities like nitrogen, so the reaction is unlikely to be quite that simple. 

Originally published on Live Science.

  • Ben
    "... When carbon burns in oxygen, that reaction produces carbon dioxide and water.."
    'Water'? That would be interesting. With just carbon and oxygen present, where did the hydrogen necessary for water come about?
  • JeetsN123
    I once saw a Youtube video where a guy burned diamonds, captured the CO2, and then used it to make carbonated water in a Sodastream! It's a very fun video.
  • Chem721
    Ben said:
    With just carbon and oxygen present, where did the hydrogen necessary for water come about?

    Technically, with a diamond, wouldn't the very terminal carbons of the carbon-matrix which are in contact with atmosphere contain a hydrogen atom, as the carbon-carbon tetrahedral structure must end at that point? Either that, or perhaps a hydroxyl group. Hydrogen sounds most likely. Certainly would only produce an ultra-trace of water, but an ultra-trace is not nothing!

    More importantly, as I think of "ideal" diamonds being a crystal of pure carbon, each atom in sp3 orbital links to four others, if it is pure and without cracks, aren't you looking at a single molecule of carbon, since all of it is covalently bonded? This is the ideal of course. Inclusions muck up the notion, but not if they are trapped and there are no surface-to-surface cracks in the diamond, it seems like each could be a single "molecule" of carbon.

  • McRa1e
    I am also having this question in my mind MyBalanceNow.
  • Uncle Al
    Diamond is s stable to 1000 °C in air, 1500 °C in inert or reducing atmosphere. No glow to ~1000 °C re Debye temperature. If you drop a really hot diamond into liquid oxygen, it skittles around burning.

    However, in contact with carbiding metals, diamond catalyticaily decomposes to graphite at room temperature, If you put some diamond dust on your finger and draw ia across molybdenum, you can see the immediate darker grey streak from molybdenum carbide.

    A poorly cut diamond will cleave into thin triangles with hardly more than a brisk tap.