[extropy-chat] Volcanic diamond eruptions

[John]

Hi Robert,

I was having a search around and found this;

"The diamond phase of carbon is metastable with respect to the graphitic phase under normal conditions; that is, graphite is thermodynamically favored over diamond (?G = ?2.99 kJ / mol). However, the rate of conversion from diamond to graphite is extremely slow due to the presence of a large kinetic barrier to this rearrangement. At room temperature, it would take an extremely long time (possibly more than the age of the Universe) for an appreciable amount of diamond to decay into graphite."

I also found an article titled "Size Dependence of Structural Metastability in Semiconductor Nanocrystals" from Science. I've posted it to you off the list.

Best wishes,
John
  ----- Original Message ----- 
  From: Robert Bradbury 
  To: ExI chat list 
  Sent: Monday, September 18, 2006 11:45 AM
  Subject: Re: [extropy-chat] Volcanic diamond eruptions




  On 9/18/06, John K Clark <jonkc at att.net> wrote:

    I realize that, I also realize that if the volcano didn't transport the
    diamonds from very deep in the earth to the surface much more rapidly than
    normal volcanoes the diamond would be turned into graphite.  I can see no 
    way such a incredibly explosive event would result in a "small volcano". I
    still don't get it.



  I think the key phrase from the article is "When a kimberlite pipe is emplaced, the surface expression is that of a small explosive volcanic eruption consisting of fragments and hot gases (pyroclastic). This volcanic explosion results in the formation of a small volcanic edifice consisting of a crater (Maar) and a pyroclastic (tuff) ring. Kimberlite volcanoes have not been documented mostly because they tend to be small in size and are easily eroded."

  It could have been a "large" volcano but one which eroded relatively quickly.  Most volcanoes we are aware of today are *very* young in geological terms.  You also have to deal with the size of the fracture through which  the pipe is forming.  If it doesn't open up the final volume of the volcano will be constrained (at the point at which the strength of the cooling surface material balances the subsurface pressure).  The large traps are not good examples as they most likely involved very large fractures representing the release of large amounts of material over long periods of time (presumably allowing the decay of any diamonds).  All releases of subsurface material do not result in "volcanoes" as evidenced by deep sea vents.  It is a complex interaction between the area through which the surface is being accessed and the composition of the material being thrust to the surface (in terms of rock and gas composition).  I am reasonably sure the composition and timing has to be such that contact of the diamond with oxygen has to be minimized.  I believe that diamond will oxidize (burn) at temperatures above 800 deg. C resulting in CO2.  As the temperatures of most magmas is significantly above that it may be true that a significant fraction of diamonds are being completely vaporized in typical surface volcanoes.  An open question might also be the conditions under which C + 2H2O --> 2H2 + CO2.  So bringing diamond to the surface might have to worry not only about exposure to oxygen but exposure to water. 

  An interesting question in my mind would be why one doesn't find diamonds in rapidly upthrust rocks subjected to rapid erosion to remove the surface material (say the Himalayas)?  Perhaps they are there but still many km beneath the surface due to the erosion requirements. 

  The fact that I did find interesting that I was unaware of was the metastable state of diamond and that it will revert to graphite.  I'd be interested in knowing the conditions that determine when that happens and whether it limits the longevity of diamondoid nanostructures. 

  Robert




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