Limit to the size of a diamond?

While reading a SciFi short the author descirbed a moon-sized diamond. I was wondering, is there any restriction on how large a diamond could be?

Depending on the circumstances, at some size it would just collapse into a neutron star.

Hmmm… okay, let’s see. At some point before that, I presume that gravitational force would be strong enough to induce carbon fusion at the heart of the diamond… making it a ‘carbon star’ of a type that AFAIK has not been observed. Somebody else can probably beat that though.

Next? :smiley:

Yeah, but it’s probably an I3, I always think it’s tacky to go for the moon-sized diamonds with obvious flaws over the flawless mountain sized diamonds.

In order to form a diamond, you have to put a load of carbon together, then subject it to temperature and pressure*, which means that your diamond must start off as part of a larger mass; this larger mass would obviously mean that only a portion of your absolute mass limit (before fusion occurs) is going to end up as diamond.
*Actually not necessarily true; diamonds can be ‘grown’ by vapour deposition, but I think it would take quite an exotic set of circumstances for anything sizeable, pure and single-crystal to naturally form that way.

Wasn’t there a diamond star discovered (and called ‘Lucy’ after the song)?

I honestly thought you were thinking of 2010, by Arthur C. Clarke, when I first read this… but you’re right.

I thought of carbon fusion, but I thought that it could be avoided if the temperature of the diamond was kept low. Pressure alone should not induce fusion.

Lucy?

C’mon, a diamond that big should be named after Fran Drescher, or maybe Liberace.

For those of us who simply can’t afford a star sized diamond, what is the largest chuck of cubic zirconium in the universe?

Well, at some point, gravitational forces are going to cause the crystalline structure to shear. So I don’t think you’d have a single moon-sized crystal, but rather a moon-sized ball of diamond crystals, some of which are very large. Still, looking at this, diamond has a pretty high compressive strength. Something like 5,000,000 kg/cubic centimeter. With a density of 3.51 g/cc, then on Earth, it seems as though you could build a diamond pillar something like 14,000km high (in the unlikely case I haven’t screwed up the math). So based just on compressive strength (and ignoring all the material science issues of which I’m totally ignorant), it looks like an Earth-sized ball of diamond isn’t out of the question.

But realistically, that’s going to more than a couple of month’s salary.

Diamond Planets

:cool: Somehow, I don’t think the British royal family is worried about their crown jewels depreciating any time soon.