[meteorite-list] Meteorite Impact Creates New Mineral

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:27:53 2004
Message-ID: <200311260259.SAA03505_at_zagami.jpl.nasa.gov>

http://www.abc.net.au/science/news/stories/s997056.htm

Meteorite impact creates new mineral
Heather Catchpole
ABC Science Online (Australia)
November 26, 2003
 
A new mineral made by a meteorite smashing into the Earth has been found
by Chinese researchers.

They said their discovery of a new form of chromite could teach scientists
more about the strength of meteorite impacts and how deep in the Earth
minerals are born.

Researchers led by Ming Chen of the Chinese Academy of Sciences published
details of the new mineral, which was formed at high pressure and
temperature, in this week's issue of the Proceedings of the National
Academy of Sciences.

The new form of chromite is an ore of the metal chromium, which is found at
meteorite impact sites as well as deep in the Earth's mantle, the layer of
rock that sits directly below the Earth's crust.

The researchers found the new mineral in shock veins formed by the impact
of the Suizhou meteorite on China in 1986. The shock of the impact created
temperatures of about 2000°C and pressures like those at 600 kilometres
below the Earth.

The researchers also made a version of the new mineral in the lab. They did
this by using a laser to subject the mineral to intense heat while
squashing it under a diamond anvil.

Researcher Professor Hugh O'Neill of the Research School of Earth Sciences
at the Australian National University in Canberra, said the new find was
interesting.

"This potentially gives us clues to the orbital velocities of two bodies
that come together to produce these shock collisions."

The researchers calibrated how the crystal form of chromite changed with
increasing pressure, to create a kind of Earth-based barometer or pressure
gauge. They said this could be used not only to gauge the strength of
meteorite impacts, but also to gauge the pressure at which rocks formed
over an important range throughout the Earth's mantle.

But O'Neill, whose team has synthesised a different, more magnesium-rich
version of chromite, doubted the calibrations could provide a comprehensive
depth gauge for rocks, saying that this was maybe "stretching the results a
little too far".

"At depths equivalent to the pressures they are talking about you don't
find this mineral. It reacts to form garnet," O'Neill told ABC Science
Online.

Chromite is normally only found at depths of about 80 kilometres below the
Earth's surface, where pressure is far less than the intense pressure
created by meteorite impacts.

And under the shock conditions of a meteorite impact pressure is applied and
released quickly, whereas in the Earth chromite is under continuous pressure
for millions of years, O'Neill said.

Under natural conditions chromite was likely to react with other minerals,
like magnesium and iron, to form a new mineral, he said.

Despite this qualification, O'Neill called the find "rare", and said that
the researchers would have the chance to name the new mineral.
Received on Tue 25 Nov 2003 09:59:02 PM PST