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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 3 Feb 2010 17:23:46 -0800 (PST)
Message-ID: <201002040123.o141Nk1x011759_at_zagami.jpl.nasa.gov>

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
Received on Wed 03 Feb 2010 08:23:46 PM PST