The hardest substance produced by life forms

river said:
None

I'm just putting it out there.

Although I find this fascinating.

I'm sure not many were aware of this fact.
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Well, since there's nothing to discuss really, why don't you ask the mods to lock the thread.
 
I'm pretty sure that posting links with no intention of discussion is just spamming.
 
You posted a random link and admitted you had no intention of wanting a discussion about it.
 
@OP: Is that spamming? Or simply casting your line from the stern of the boat, and using the auxiliary low-speed motor, attempt to catch dinner?
fishing.gif
 
:DQUOTE="river, post: 3322491, member: 179019"]None

I'm just putting it out there.

Although I find this fascinating.

I'm sure not many were aware of this fact.[/QUOTE]

OK, then let me, as a scientist, do the job for you.:D

The reference is to the teeth of the chiton, which, it seems, are made from magnetite, Fe₃O₄. I certainly did not know this and was interested to learn it.

I looked up the hardness of mineral magnetite, on the Mohs scale. It varies from 5 to 6.5. Mammalian tooth enamel, which is hydroxyapatite, has a Mohs hardness of 5. So comparable with the softer end of the range for magnetite. Frustratingly, the New Scientist article fails to give us the results of any hardness measurements on the magnetite in the chiton's teeth - all part of its somewhat dumbed-down editorial policy, no doubt.

From looking at the Wiki article on magnetite, it seems this is far from the only occurrence of magnetite in biological systems: https://en.wikipedia.org/wiki/Magnetite , which suggests to me that there may be some ancient piece of biochemistry involving iron minerals buried in the history of life. Black smokers and all that perhaps? - But I speculate. Maybe someone more knowledgeable on early lifeforms can comment on this.
 
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The scientific article (in Nature) also doesn't immediately give any figure for hardness or toughness of chiton teeth, although it does discuss how composite materials makes these teeth tougher than the simples structures of inorganic minerals.
http://www.researchgate.net/profile...iton_tooth/links/09e41511c0d00a4c8c000000.pdf

A different article gives numbers for hardness:
The magnetite veneer has a modulus ranging from 90 to 125 GPa and a corresponding hardness ranging from 9 to 12 GPa. To the best of our knowledge, these values represent the highest modulus yet reported for a biomineral22. The hardness is notably about 3 times higher than that of enamel and nacre, which exhibit indentation hardness and modulus of 3 – 4 GPa and 65 – 75 Gpa22, respectively, making this material exceptionally well suited for the continuous scraping activity of the radular teeth.
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http://www.sciencedirect.com/science/article/pii/S136970211070016X

And reference 22, is the 1995 source material for the claim.

http://rspa.royalsocietypublishing.org/content/450/1938/123 (No free version located)

Hardness numbers obtained by different methods cannot be compared directly, but my reading sugegsts:
Indentation Hardness 9-12 GPa ~ Vickers Hardness 900-1200 kgf/mm^2 ~ Mohs scale 5-6.5

Baddeleyite (Zirconia) has a Mohs hardness of 6.5 and Figure 6 from the third reference suggests they have nearly equal indentation hardness.
 
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rpenner said:
The scientific article (in Nature) also doesn't immediately give any figure for hardness or toughness of chiton teeth, although it does discuss how composite materials makes these teeth tougher than the simples structures of inorganic minerals.
http://www.researchgate.net/profile...iton_tooth/links/09e41511c0d00a4c8c000000.pdf
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Aha many thanks. So the New Scientist people got the whole thrust of the article wrong: typical journalists. Actually it seems chiton teeth are a well known "model system" for investigating what they call "matrix-modulated mineralisation".

I thought the most interesting sentence was: " The outstanding fracture toughness and wear resistance of the tooth results from the organic–inorganic interfaces over multiple levels of hierarchy, which deflect and arrest cracks".

So in fact it is the composite nature of these teeth, rather than the mere fact the mineral component is magnetite, that gives them their unique aptitude for the task.
 
rpenner said:
The scientific article (in Nature) also doesn't immediately give any figure for hardness or toughness of chiton teeth, although it does discuss how composite materials makes these teeth tougher than the simples structures of inorganic minerals.
http://www.researchgate.net/profile...iton_tooth/links/09e41511c0d00a4c8c000000.pdf
Click to expand...

Aha many thanks. So the New Scientist people got the whole thrust of the article wrong: typical journalists. Actually it seems chiton teeth are a well known "model system" for investigating what they call "matrix-modulated mineralisation".

I thought the most interesting sentence was: " The outstanding fracture toughness and wear resistance of the tooth results from the organic–inorganic interfaces over multiple levels of hierarchy, which deflect and arrest cracks".

So in fact it is the composite nature of these teeth, rather than the mere fact the mineral component is magnetite, that gives them their unique aptitude for the task.
rpenner said:
It's both the hardness and the toughness.
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Good point.
 
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