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

[Ron Baalke]

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."