[meteorite-list] Meteorite Yields Carbon Crystals Harder Than Diamond

From: Göran Axelsson <axelsson_at_meteoritecentral.com>
Date: Thu, 04 Feb 2010 14:18:38 +0100
Message-ID: <4B6AC92E.3010107_at_acc.umu.se>

This article seems to be lacking in two parts.

As already stated, the pressure from atmosphere entry is too low to
create diamonds.

The second part I reacted to was the statement
 "The crystals were raised more than 10 ?m above the polished surface,
which meant they were harder than the diamonds in the polishing paste."

That is plainly wrong. If a hard mineral like ordinary diamonds is
embedded in a softer material, for example some silicate minerals then
the silicates will be removed at a faster pace than the harder diamonds
which rises above the surrounding surface.

Maybe it's just a problem with the interpretation of the original
article by the physorg writer....
Oh, I think it is. The abstract never claims higher hardness than
diamond, "... were not easily polishable by a diamond paste and would
therefore imply larger polishing hardness."
I guess that the part about atmosphere is also an error made by physorg,
not the original researcher. I read it as "... larger polishing hardness
[than surrounding material]."

Original abstract at :
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4Y4XCTH-3&_user=10&_coverDate=02%2F15%2F2010&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d8d1010a5c82833bfc75265887d7cf8a

Too bad I can't access the full article. :-(

/G?ran

Ron Baalke wrote:
> http://www.physorg.com/news184402061.html
>
> Meteorite yields carbon crystals harder than diamond
> by Lin Edwards
> physorg.com
> February 3, 2010
>
> (PhysOrg.com) -- Two new types of ultra-hard carbon crystals have been
> found by researchers investigating the ureilite class Haver? meteorite
> that crashed to Earth in Finland in 1971. Ureilite meteorites are
> carbon-rich and known to contain graphite and diamonds.
>
> The super-hard diamonds were created when graphite in the meteorite
> experienced the intense heat and pressure of entering the Earth's
> atmosphere and crashing into the ground. The graphite layers would
> have been heated and shocked enough to create bonds between them, in
> much the same way as humans manufacture
> diamonds.
>
> The new carbon crystals were too small to test for precise hardness but
> they are known to be harder than normal diamonds because the researchers
> found them by using a diamond paste to polish a slice of the meteorite.
> The crystals were raised more than 10 ?m above the polished surface,
> which meant they were harder than the diamonds in the polishing paste.
> The researchers had seen carbon crystals that resisted the diamond
> polishing in one direction before, but the new crystals were unaffected
> when polished in every direction.
>
> The scientists then used an array of mineralogical instruments,
> including microscopy, spectroscopy and energy-dispersive X-rays among
> others, to study the structure of the crystals. This allowed them to
> identify them as representing two new carbon polymorphs or diamond
> polytypes.
>
> One is an ultra-hard rhombohedral carbon polymorph similar to diamond,
> while the other is a 21R diamond polytype ultra-hard diamond. The
> existence of ultra-hard diamonds had been predicted decades ago, but
> they have never before been found in nature. The novel form consists of
> fused graphite sheets similar to artificial diamond.
>
> Professor Tristan Ferroir, leader of the research team from the
> Universit? de Lyon in France, said the discovery was accidental, but
> they had thought an examination of the meteorite would "lead to new
> findings on the carbon system."
>
> Professor Ferroir said there is currently no way to compare the
> structure of the new crystals to boron nitride and lonsdaleite, the
> artificially manufactured ultra-hard diamonds, but the findings help
> scientists gain a better understanding of carbon polymorphs and give
> them new materials to investigate and perhaps synthesize. They also
> show the carbon system is more complex than previously thought.
>
> The findings on the new diamond were published in the Earth and
> Planetary Science Letters journal on February 15.
>
> More information:* http://dx.doi.org/10.1016/j.epsl.2009.12.015
> ______________________________________________
> Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
>
Received on Thu 04 Feb 2010 08:18:38 AM PST