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 µm 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. :-(
/Göran
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 Haverö 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 µm 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
Université 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
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