[meteorite-list] Rock or Meteorite? Ask The Prof

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:09 2004
Message-ID: <200207241836.LAA29595_at_zagami.jpl.nasa.gov>

http://news.mywebpal.com/partners/899/public/news335015.html

Rock or meteorite? Ask the prof
By Sean Murphy
The Norman Transcript (Oklahoma)
July 23, 2002

In 1962, a Nigerian farmer was trying to chase crows from his corn field
when he heard a tremendous explosion and saw a 40-pound meteorite land 10
feet from where he was standing.

The meteorite turned out to be one of only 26 known Mars meteorites, and a
small piece of it is housed at the University of Oklahoma's Sarkeys Energy
Center.

David London, a professor of geology at OU who obtained the piece from a
dealer, said the Mars meteorites likely originated when a meteoroid slammed
into the surface of Mars with enough force to dislodge portions of the
planet. Those pieces then likely spent several million years floating
through space before eventually being drawn into the earth's gravitational
field and landing in various locations around the globe.

"Martian meteorites are exceedingly rare," London said. "Especially when you
think about the probability of any of this happening."

London said the Martian meteorites were determined to be part of the planet
after researchers examined the gases that were emitted when they were heated
and then compared those gases to the known atmosphere of Mars.

"The gases given off match the Martian atmosphere as determined by the
Viking Mars lander," London explained. London said the Martian meteorites
also exhibit a unique loss of crystalline structure that occurred when the
pieces were blasted off the planet's surface.

"The atoms in them were so violently moved that they lost their crystal
pattern and became disorganized," he said. "It's an odd feature, and
geologists don't get to see these features in earthly rocks."

Examining rocks

Although London admits he is not an expert on Martian meteorites, he can
certainly tell the difference between a "regular" meteorite and a rock
someone finds in their back yard. In fact, in the 19 years he has been at
OU, London said he typically receives two to three calls a week from people
who have found strange or unusual rocks they think might be meteorites.

On Tuesday, London examined a rock sample brought in by Anita Robinson of
Cashion. She found a unique-looking rock while doing some off-road driving
with her husband near Gunnison, Colo., earlier this month. Robinson said the
dark-colored rock immediately grabbed their attention because it was
perfectly round and embedded in the center of a light-colored section of the
mountain.

"It just stuck out like a sore thumb because the color was so dramatic,"
Robinson said.

A quick analysis of the rock with a hand-held magnifying glass told London
the rock did not feature some of the elements usually contained within a
meteorite, namely flecks of iron or nickel. He told Robinson he could
conduct a more intense analysis for $35 using an electron microscope, but
said he was confident the rock was not a meteorite.

"We thought the chances were pretty slim," Robinson admitted. "We're not
surprised, but maybe a little disappointed."

Although London said he has yet to see a real meteorite brought in to him
for examination, he doesn't rule out the possibility.

"No one has brought me a found meteorite ... but it could happen any day,"
he said.

Two kinds

London said there are two basic kinds of meteorites - metallic meteorites
that are mostly iron and stony meteorites that have a "fusion crust" on the
surface that develops when the surface melts to glass during its plunge
through the earth's atmosphere and then hardens before it hits the ground.
Both types of meteorite are on display at Sarkeys.

Most meteorites are discovered in Antarctica and the Saharan desert, London
said, where they stand out easily. If there is a dark-colored rock in the
middle of a sand dune or an ice field, there is little doubt where it came
from.

Even though no one has yet brought him a meteorite, London said he enjoys
meeting people and hearing their stories of how they came into possession of
these unique rocks.

"I'm happy to do it," he said. "Anita learned a little bit today of what a
meteor should look like."

"That's satisfying."

And while London said he will examine any rock free of charge that someone
suspects is meteorite, he said he doesn't like to do analysis over the
phone, and he will rarely go and look at a rock in the field.

"It's one thing when people bring me a sample," he said. "It's another to
rent a backhoe and dig something out."
Received on Wed 24 Jul 2002 02:36:30 PM PDT