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<DIV><FONT face=Arial size=2>Hi Robert,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I was having a search around and found
this;</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>"The diamond phase of carbon is </FONT><A
title=Metastable href="http://en.wikipedia.org/wiki/Metastable"><FONT face=Arial
size=2>metastable</FONT></A><FONT face=Arial size=2> with respect to the
graphitic phase under </FONT><A title="Standard temperature and pressure"
href="http://en.wikipedia.org/wiki/Standard_temperature_and_pressure"><FONT
face=Arial size=2>normal conditions</FONT></A><FONT face=Arial size=2>; that is,
graphite is thermodynamically favored over diamond (</FONT><A
title="Gibbs free energy"
href="http://en.wikipedia.org/wiki/Gibbs_free_energy"><FONT size=2><FONT
face=Arial>Δ<I>G</I></FONT></FONT></A><FONT face=Arial
size=2> = −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."</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I also found an article titled "</FONT><FONT
face=AkzidenzGrotesk-Bold size=5><FONT face=Arial size=2>Size Dependence of
Structural Metastability in </FONT><FONT face=Arial size=2>Semiconductor
Nanocrystals" from Science. I've posted it to you off the
list.</FONT></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=AkzidenzGrotesk-Bold size=5><FONT face=Arial size=2>Best
wishes,</FONT></FONT></DIV>
<DIV><FONT face=AkzidenzGrotesk-Bold size=5><FONT face=Arial
size=2>John</FONT></DIV></FONT>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=robert.bradbury@gmail.com
href="mailto:robert.bradbury@gmail.com">Robert Bradbury</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=extropy-chat@lists.extropy.org
href="mailto:extropy-chat@lists.extropy.org">ExI chat list</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, September 18, 2006 11:45
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [extropy-chat] Volcanic
diamond eruptions</DIV>
<DIV><BR></DIV><BR>
<DIV><SPAN class=gmail_quote>On 9/18/06, <B class=gmail_sendername>John K
Clark</B> <<A href="mailto:jonkc@att.net">jonkc@att.net</A>>
wrote:</SPAN><BR>
<BLOCKQUOTE class=gmail_quote
style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid">I
realize that, I also realize that if the volcano didn't transport
the<BR>diamonds from very deep in the earth to the surface much more rapidly
than<BR>normal volcanoes the diamond would be turned into
graphite. I can see no <BR>way such a incredibly explosive event
would result in a "small volcano". I<BR>still don't get
it.<BR><BR></BLOCKQUOTE></DIV><BR>I think the key phrase from the article
is<FONT size=2> "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."<BR><BR>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. <BR><BR>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. <BR><BR>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. <BR><BR>Robert<BR><BR></FONT>
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