[meteorite-list] Opal Found in Antarctic Meteorite (EET 83309)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 30 Jun 2016 23:47:23 +0000 (GMT)
Message-ID: <201606302347.u5UNlOJw025872_at_zagami.jpl.nasa.gov>

https://cosmosmagazine.com/space/opal-found-in-antarctic-meteorite

Opal found in Antarctic meteorite
Cosmos Magazine
June 28, 2016

Planetary scientists show, for the first time, the gemstone in a chunk
of asteroid. Belinda Smith reports.

Planetary scientists have found gemstones that are literally out of this
world - and thrown more weight behind the idea that asteroids ferried
water around the solar system.

Tiny fragments of opal were spotted in a meteorite EET 83309, which was
picked up off the ice in east Antarctica - the second time a meteorite
has been found containing the gemstone. (The first was a Martian meteorite,
reported in July last year.)

The work was presented by the UK's Birkbeck College London's Hilary Downes
at the Royal Astronomical Society meeting in Nottingham.

On Earth, opals form when silica in a watery solution becomes wedged in
cracks between rocks. Over millions of years, the silica hardens to become
the shimmery coloured rock we prize today.

The key here, and what has planetary scientists excited, is opal needs
water to form - it can even hold up to 30% water. So a meteorite carrying
opal means it came in contact with water millions of years ago.

EET 83309 isn't a nice, rounded rock. About 4 x 4 x 2.4 centimetres, it's
a conglomerate, a fragment of a meteorite containing lots of smaller fragments
of other meteorites. It's thought it was once part of a parent asteroid
that copped plenty of hits from bits of rock floating around the solar
system. Some of those rocks embedded themselves into the asteroid.

One or more of these impacts, Downes believes, brought water ice to the
asteroid and allowed the opal to form.

"The pieces of opal we have found are either broken fragments or they
are replacing other minerals," she says.

"Our evidence shows that the opal formed before the meteorite was blasted
off from the surface of the parent asteroid and sent into space, eventually
to land on Earth in Antarctica."

Given the meteorite landed on water ice, and may have been sitting out
in the open for millions of years, could the opal have formed after it
landed?

Downes and her colleagues doubt it. Although the opal interacted a little
with Antarctic water, there was more "heavy water" (water where one or
both hydrogen atoms has been replaced with a slightly heavier deuterium
atom) in the opal and meteorite than in Earthly water.

"This is more evidence that meteorites and asteroids can carry large amounts
of water ice," Downes says.

"Although we rightly worry about the consequences of the impact of large
asteroids, billions of years ago they may have brought the water to the
Earth and helped it become the world teeming with life that we live in
today."
Received on Thu 30 Jun 2016 07:47:23 PM PDT