[meteorite-list] New Australian fall

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 18 Sep 2009 22:15:23 -0500
Message-ID: <C1C03C201536464591F4FF92F54260B5_at_ATARIENGINE2>

Hi, Jason, List

    The word "eucrite" comes from the Greek
and means "easily recognized." It was coined
to describe terrestrial basalts and only later
was it applied to meteorites, and to the most
common of achondrites. It is no longer used
for Earthly rocks.

    They are basalts from lava flows on the
surface of a differentiated body. They're just
ordinary basaltic rocks, only from somewhere
other than Earth.

    The oxygen data is tricky. You plot the slope
of the ratios of O17 or O18 to O16 for each rock.
Those that land on the same slope are not always
from the same body, because different bodies may
have the same oxygen ratios.

    For example, aubrites and lunar achondrites
plot on the terrestrial ratio slope, meaning that
the Earth and the Moon and the Wherever-the-
aubrites-came-from all have the SAME oxygen
ratios. Eucrites from Vesta plot along a slope
all their own.

    I assume what the reporter said of what Bland
said meant that this eucrite does not plot on the
Vestan slope. We have no idea of what slope it
plots on; as is usual with press reports, there is
no usable information in them. What slope did
it plot on? Who knows? Bland does; we're guessing
without data. If he knew the body it came from,
it would be big news and he would have told it.
Shouted it, actually...

    So, it is a basalt lava flow from the crust of
SOME other body than Vesta or a Vestoid, but
otherwise not known. It's a breccia with clasts
so that body has an impact-altered surface. We
have exsolution so it was (once) a big enough body
to have cooled slowly.

    Equally vague and useless are the press release
level comments about "inner solar system" orbits.
Numbers are the only thing with meaning. Semi-major
axis in AU, please, eccentricity, etc. NOT knocking
the scientist speaking, only the reporter listening to
stuff he knows nothing about. It's like sending your
five-year-old to talk to your Congressman, and then
come back and tell you what he said about health
care reform. Meaningless. The "Scientific" American
article is, if anything, more vague.

    The mention of Bottke and SWR studies probably
means the study that showed that many members
of the inner asteroid zone were tossed there from the
very "inner" solar system, <0.5 AU, particularly the
big iron asteroids. This little eucrite could be a chunk
of the largely battered-away former crust of Mercury,
for example. Put a lander on Mercury and measure
the oxygen ratios and we'll know.

    As usual, too little data for ANY conclusion. The
connection with the Bottke study is likely purely
hypothetical. In other words, a guess. There's nothing
you can say about nothing.


Sterling K. Webb
--------------------------------------------------------------------------
----- Original Message -----
From: "Jason Utas" <meteoritekid at gmail.com>
To: "Meteorite-list" <meteorite-list at meteoritecentral.com>
Sent: Friday, September 18, 2009 8:45 PM
Subject: Re: [meteorite-list] New Australian fall


Good point; and seeing as such meteorites haven't been
reclassified/re-typed, it seems as though this brings up a very valid
flaw in the classification system of basaltic achondrites. Perhaps
there are some scientists out there who can shed some light on why
meteorites such as these are called Eucrites when they are apparently
from different parent bodies. I'd be curious of the general
scientific opinion of the current classification scheme; is it
adequate or should there be more, if not classes, at least meteorites
deemed 'ungrouped.'
Jason

On Fri, Sep 18, 2009 at 6:37 PM, Michael Fowler <mqfowler at mac.com>
wrote:
>> And in case you didn't check the met-bull, the Bunburra Rockhole
>> meteorite has been classified as a typical Eucrite.
>> He stated that said meteorite is not from Vesta, but Eucrites are
>> widely accepted to have come from Vesta.
>> I suppose we don't have solid proof of that yet, but it is generally
>> accepted to be true, based on reflected light analyses.
>> Go figure.
>> Jason
>
> Hi Jason,
>
> Sorry if I ruffled your feathers earlier.
>
> I did check the met bulletin, and it is described as: " meteorite is a
> basaltic eucrite monomict breccia "
>
> http://tin.er.usgs.gov/meteor/index.php?code=48653
>
> However I note that many meteorites are not correctly classified on
> their
> first appearance in the Met Bul, including of course Ibitria, which is
> still listed as a Eucrite Monomict, even though we know it is not from
> Vesta,
>
> http://tin.er.usgs.gov/meteor/index.php?sea=ibitira&sfor=names&ants=&falls=&valids=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&rect=&phot=&snew=0&pnt=no&code=11993
>
> However back to, Bunburra Rockhole, can someone comment or whether the
> mineral composition as stated in the met bul is consistent, or
> anomalous for
> a eucrite?
>
> Mineral compositions: Pyroxene, Fs62.5Wo3.6 (Fe/Mn-31.1) with augite
> (Fs27.7Wo43.0) lamellae; plagioclase, An84.1 to An88.2.
>
> Of course, the final word is probably the O isotope work, which Dr
> Bland
> says has already been done, although I couldn't find any additional
> reference.
>
> Thanks,
>
> Mike
>
>
>
>
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Received on Fri 18 Sep 2009 11:15:23 PM PDT