[meteorite-list] New Australian fall

From: cdtucson at cox.net <*cdtucson_at_meteoritecentral.com*> Date: Sat, 19 Sep 2009 13:00:01 -0700 Message-ID: <20090919160001.9K92Y.268724.imail_at_fed1rmwml44> · cdtucson_at_meteoritecentral.com

--
Carl or Debbie Esparza
IMCA 5829
Meteoritemax
---- "Sterling K. Webb" <sterling_k_webb at sbcglobal.net> wrote: 
> 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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