<blockquote>
  <p>It is bond strength, not hardness, that determines how easily oxygen
  can attack and burn a material, allowing me to burn a diamond in a
  pool of liquid oxygen resting in a block of graphite.</p>
</blockquote>

<p>Diamond is hard because its bonds form an inflexible, three-dimensional lattice. However, the strength of these bonds themselves is not even as strong as graphite, for example. Graphite has much stronger bonds, but they create "sheets," which can slide around, making graphite softer but harder to burn.</p>

<p><sup><a href="http://www.popsci.com/diy/article/2009-08/burn-diamonds-torch-and-liquid-oxygen">(source)</a></sup></p>

<p>Indeed, <a href="http://io9.com/how-and-why-to-make-a-diamond-burn-637183425">people have burned diamonds before by putting them in tubes of pure oxygen</a>.</p>

CC BY-SA 3.0
2014-04-16T21:19:15.420Z
2014-04-16T21:19:15.420Z
Doorknob
<p>For those confused about the title, there's a joke that every moderator has a "diamond hammer" (diamond from the little <code>♦</code> by the username). In a <a href="http://chat.stackexchange.com/transcript/11540?m=14796232#14796232">chat discussion</a>, it was brought to my attention that a diamond <em>can</em> burn (which makes total sense because it's pure carbon) after I got a notification in orange in the topbar of SE.</p>

<p>Anyway my question is <strong>why can something so durable be able to burn?</strong> I would imagine that there would be a relationship between flammability and durability, especially since metal cannot burn.* Is it just a coincidence that most people think hard == inflammable? Why <em>can</em> diamond burn?</p>

<p>*It can burn when oxidized IIRC.</p>

CC BY-SA 3.0
2016-04-05T08:04:21.133Z
The generalizations make your question a bit silly. Pure metals are all over the hardness and toughness scale - gold is very soft and malleable, uranium is quite hard, but still malleable, chromium is the hardest pure metal, sodium is weak... and all of them have quite different chemical properties. Gold is one of the most inert elements, and is very stable. Uranium is very reactive and burns quite well - but it's even more reactive with e.g. water. Chromium is very reactive, but forms a protective oxidised layer at room temperatures. Sodium burns readily in water at room temperatures.
Luaan
CC BY-SA 3.0
2014-07-07T07:05:51.687Z
The real question here is why would anyone waste a diamond by burning it?
f.thorpe
CC BY-SA 3.0
2014-04-16T21:16:49.750Z
It doesn't really surprise me, as diamond is pure carbon in a densely packed crystal lattice. By adding enough heat you'll release carbon atoms from the lattice, and when oxygen is present CO2 will form. It'll take a lot of heat though, I guess (that's why this is only a comment, not an answer, although I'd be glad to make it into one if you think it's sufficient).
hugovdberg
CC BY-SA 3.0
2014-04-17T22:15:40.720Z
This question appears to be more about the chemistry of diamonds than the "earth science" aspects of it.
Tom Au
CC BY-SA 3.0
2014-04-18T01:15:15.897Z
Yeah, this would definitely sit better at http://chemistry.stackexchange.com than here, it's got nothing to do anything geological, really. Also, I find the joke at the start kind of more distracting and confusing than funny, but maybe that's just me.
naught101
CC BY-SA 3.0
2014-04-18T01:15:42.910Z
This question appears to be off-topic because it is about chemistry
naught101
CC BY-SA 3.0
2014-04-18T01:32:00.340Z
[Related Meta discussion](http://meta.earthscience.stackexchange.com/questions/66/where-is-the-boundary-between-geology-and-chemistry)
Anonymous Penguin
<geology><geochemistry><mineralogy><diamond>
Why is my ♦ hammer (i.e. diamond) so durable, but it can burn?
Anonymous Penguin
# Why is my ♦ hammer (i.e. diamond) so durable, but it can burn?

(Asked by: username_0 on 2014-04-16)

For those confused about the title, there's a joke that every moderator has a "diamond hammer" (diamond from the little `♦` by the username). In a [chat discussion](http://chat.stackexchange.com/transcript/11540?m=14796232#14796232), it was brought to my attention that a diamond *can* burn (which makes total sense because it's pure carbon) after I got a notification in orange in the topbar of SE.

Anyway my question is **why can something so durable be able to burn?** I would imagine that there would be a relationship between flammability and durability, especially since metal cannot burn.\* Is it just a coincidence that most people think hard == inflammable? Why *can* diamond burn?

\*It can burn when oxidized IIRC.

**Tags:** geology, geochemistry, mineralogy, diamond

> **Comments:**
> **username_3**: It doesn't really surprise me, as diamond is pure carbon in a densely packed crystal lattice. By adding enough heat you'll release carbon atoms from the lattice, and when oxygen is present CO2 will form. It'll take a lot of heat though, I guess (that's why this is only a comment, not an answer, although I'd be glad to make it into one if you think it's sufficient).  
> **username_4**: This question appears to be more about the chemistry of diamonds than the "earth science" aspects of it.  
> **username_5**: Yeah, this would definitely sit better at http://chemistry.stackexchange.com than here, it's got nothing to do anything geological, really. Also, I find the joke at the start kind of more distracting and confusing than funny, but maybe that's just me.  
> **username_5**: This question appears to be off-topic because it is about chemistry  
> **username_0**: [Related Meta discussion](http://meta.earthscience.stackexchange.com/questions/66/where-is-the-boundary-between-geology-and-chemistry)  
> **username_2**: The real question here is why would anyone waste a diamond by burning it?  
> **username_1**: The generalizations make your question a bit silly. Pure metals are all over the hardness and toughness scale - gold is very soft and malleable, uranium is quite hard, but still malleable, chromium is the hardest pure metal, sodium is weak... and all of them have quite different chemical properties. Gold is one of the most inert elements, and is very stable. Uranium is very reactive and burns quite well - but it's even more reactive with e.g. water. Chromium is very reactive, but forms a protective oxidised layer at room temperatures. Sodium burns readily in water at room temperatures.  

---

## 1 answers

### Answer by username_6 on 2014-04-16. Score: 11 | Accepted answer

> It is bond strength, not hardness, that determines how easily oxygen
> can attack and burn a material, allowing me to burn a diamond in a
> pool of liquid oxygen resting in a block of graphite.

Diamond is hard because its bonds form an inflexible, three-dimensional lattice. However, the strength of these bonds themselves is not even as strong as graphite, for example. Graphite has much stronger bonds, but they create "sheets," which can slide around, making graphite softer but harder to burn.

[(source)](http://www.popsci.com/diy/article/2009-08/burn-diamonds-torch-and-liquid-oxygen)

Indeed, [people have burned diamonds before by putting them in tubes of pure oxygen](http://io9.com/how-and-why-to-make-a-diamond-burn-637183425).


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