# Is there some idea of a largest likely intact single crystal diamond on the surface?
**URL:** https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094
**Category:** Factual Questions
**Created:** [August 23, 2024, 10:13am UTC](https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094 "2024-08-23T10:13:22Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)
#### Post date: [August 23, 2024, 10:13am UTC](https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094/1 "2024-08-23T10:13:23Z")
Triggered by this find, but I’ve wondered about it for a while. Is there thoughts on if internal stresses of diamonds brought to the low-pressure frigid surface might cause diamonds above a certain size to shatter? None of the largest found diamonds are especially large (this one is a little more than a pound) and none of the largest ones I jnow of are a neat octohedron.
> **[World’s second-largest diamond discovered in Botswana](https://www.cnbc.com/2024/08/23/worlds-second-largest-diamond-discovered-in-botswana.html)**
>
> One of the largest diamonds ever to be excavated was found in Botswana at a mine owned by Canadian firm Lucara Diamond.
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### Author:  [@Napier](https://boards.straightdope.com/u/Napier)
#### Post date: [September 5, 2024, 1:43pm UTC](https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094/2 "2024-09-05T13:43:32Z")
I don’t think the temperature change would cause it to shatter. Diamonds have extremely high thermal conductivity. The heat transfer coefficient for a fist sized object in still air is going to be pretty low. I think the Biot number, which compares the external heat transfer to the internal heat transfer, for the diamond would be small as a result. Biot number addresses whether an object will heat up quickly on the surface and the temperature change will slowly march inward toward the center, or will heat up slowly with a nearly uniform internal temperature. You need a high Biot number to get the surface to expand without the insides expanding, if you want temperature change to shatter it. With a diamond in air you have the opposite situation.
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### Author:  [@Melbourne](https://boards.straightdope.com/u/Melbourne)
#### Post date: [September 29, 2024, 2:02pm UTC](https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094/3 "2024-09-29T14:02:07Z")
Diamonds ‘above a certain size’ are likely to be shattered by the explosions used to shatter rocks for extraction – and if they aren’t, they are likely to be shattered by the rock crushers at the surface.
We’re seeing some very large diamonds now because the mines are adopting a process of doing x-ray examination of the ore _before_ it goes into the crusher. They’re still kind of rare because they have to survive the extraction.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 30, 2024, 6:49am UTC](https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094/4 "2024-09-30T06:49:17Z")
I suppose there must be practical constraints on the size of a single diamond that could form on Earth - whilst the materials are abundant, the specific combination of materials and conditions may restrict the ultimate size - crystals forming in cooling rock whilst still under pressure and not flowing, will tend to locally deplete the mineral of which they are composed, self-limiting their ultimate size.
I imagine there could be exceptions to that, but it’s probably a bell curve - most examples are like most other examples and exceptions are rarer the more exceptional they are.
It has been hypothesised that some astronomical objects might be able to form much larger diamonds than occur here on earth - the corpse of a white dwarf star, for example, may turn into one enormous diamond, supposedly.
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### Author:  [@Melbourne](https://boards.straightdope.com/u/Melbourne)
#### Post date: [October 2, 2024, 5:21am UTC](https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094/5 "2024-10-02T05:21:33Z")
It’s thought that some of the recent big diamonds that were found together were part of a 1KG (2.2lb, 5000ct) crystal that was broken during extraction.
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### Author:  [@MrDibble](https://boards.straightdope.com/u/MrDibble)
#### Post date: [October 2, 2024, 9:39am UTC](https://boards.straightdope.com/t/is-there-some-idea-of-a-largest-likely-intact-single-crystal-diamond-on-the-surface/1006094/6 "2024-10-02T09:39:47Z")
> [@Darren\_Garrison](#):
>
> Is there thoughts on if internal stresses of diamonds brought to the low-pressure frigid surface might cause diamonds above a certain size to shatter?
My thought is that variance is tiny compared to the various pressure/temp changes any sizeable diamond is likely to have encountered over the millions to [billions](https://www.sciencedaily.com/releases/2017/02/170223102126.htm) of years of its formation.
Diamond is metastable at the surface. That counts whether it’s a small or big one. It’s not going to shatter just from a pressure/temp drop, it’s going to need other stresses applied, IMO. Which, yeah, diatreme eruptions are particularly violent ones (as in - _supersonic_) so there’s a lot of other stresses there. But that’s external stresses, not internal ones.
> [@Darren\_Garrison](#):
>
> None of the largest found diamonds are especially large
See above about length of time of formation of even small diamonds. I suspect that’s the major size limiting factor - we don’t have 1-tonne diamonds because Earth hasn’t been here long enough for them to grow.
> [@Darren\_Garrison](#):
>
> none of the largest ones I jnow of are a neat octohedron
This is because they’re not just condensing one-time as single crystals out of a melt, but by zoned metasomatic growth with millennia of convection, reabsorption, coalescence around multiple centres, etc. involved.
> [@Mangetout](#):
>
> crystals forming in cooling rock whilst still under pressure
Almost all natural diamonds likely form by metasomatic (hot fluid-driven) growth by mineral replacement in the effectively-solid mantle, they’re not just growing from liquid melts like crystals in cooling lava. In other words, they were diamonds that grew in place in the upper mantle _before_ their host rocks erupted to form kimberlites/lamproites.