[meteorite-list] Flow lines on the INSIDE! Not.

From: countdeiro at earthlink.net <countdeiro_at_meteoritecentral.com>
Date: Mon, 28 Sep 2009 15:52:41 -0400 (EDT)
Message-ID: <8747564.1254167561181.JavaMail.root_at_wamui-june.atl.sa.earthlink.net>

Hi Jason, Piper, Mike and List,

Gathering my tattered cloak up to cover myself, I must say that even I, with less than a year in the game, wouldn't be so ignorant as to say I saw flow lines on the INSIDE of a specimen. What I said.. and did see.. were..and I will be a bit more descriptive here...nearly parallel, but sinuous, thin, rounded, iron lines orientated in one direction on the outside surface of a formerly concreted and rusted Nantan that I had blasted the crap out of and wirebrushed. It looks lovely. Maybe I should put it eBay and call it a 100% crusted and oriented individual...:o}

Guido

-----Original Message-----
>From: Jason Utas <meteoritekid at gmail.com>
>Sent: Sep 28, 2009 4:45 AM
>To: Meteorite-list <meteorite-list at meteoritecentral.com>
>Subject: Re: [meteorite-list] "flow lines" on weathered irons (was "question on cleaning irons")
>
>Hello Piper,
>Of course - hence the differential weathering rates of Campos ("old"
>versus "new"), to name one of many examples.
>Perhaps the best example of such weathering can be seen on irons from
>Gibeon. I unfortunately don't have a copy of Buchwald here, but if
>anyone does have access to the second volume, if they could flip
>through the Gibeon section, they would find a photograph of a
>beautiful mass of Gibeon (I forget the name of the mass) on display in
>a museum in Germany. It displays beautiful fusion crust and
>smooth-edged, shallow regmaglypts - it looks as fresh as many Sikhotes
>on the market today. Compare it to many of the larger Gibeons on ebay
>today and you'll see little-to-no resemblance. If anyone out there
>can scan a picture of said page, I'd be much obliged. It really is a
>good example.
>There are, however, a few common irons which I would never expect to
>have fusion crust: Canyon Diablo, Toluca, Odessa, and Nantan, to name
>a few. I've seen hundreds, if not thousands of examples of each, and
>I have never seen a single one of any of them that came close to being
>"fresh" enough to retain a trace of fusion crust.
>Nantan is one of the most corroded and least stable iron meteorites I
>have ever known, though Dronino's turning out to be about as bad.
>People need to learn more in order to clear up the misconception that
>all meteorites show signs of a hot, violent entry through the
>atmosphere; I see NWA's on ebay all the time that are nothing but old
>weathered fragments coated with desert varnish. Check out this
>seller:
>
>http://myworld.ebay.com/eegooblago/
>
>Almost all of his stones are covered in a 'glossy fusion crust.' Oh
>wait - those are just desert varnished fragments that have been
>weathered to hell. Most of the melt features the seller notes are due
>to sandblasting and corrosion, and s/he goes so far as to say that the
>cracks in his stones formed when they hit the ground! Anyone remotely
>familiar with meteorites and weathering processes knows that over
>thousands of years, meteorites fracture and break apart, in a manner
>completely unrelated to their having impacted the Earth.
>This seems like a very similar misconception; Guido even notes finding
>flow lines on the inside of the meteorite, having broken it open.
>There's no way there would have been any flow lines on the surface of
>the iron, never mind the inside of it. It simply isn't possible.
>Regards,
>Jason
>
>On Mon, Sep 28, 2009 at 12:47 AM, Piper R.W. Hollier <piper at xs4all.nl> wrote:
>> Hi Guido, Jason, Mike, and list,
>>
>> At 22:33 27-09-09, Jason wrote:
>>>
>>> Regardless of how well you cleaned your Nantan, whatever you found
>>> under the surface was not flow lines.
>>
>> It appears that the layers of taenite and kamacite do not always oxidize at
>> the same rate at the surface of a buried iron. This would make sense
>> intuitively, since the proportion of nickel is different. Just as nitol has
>> a differential effect on taenite and kamacite in the lab, some conditions of
>> soil chemistry might produce an analogous result in the strewn field, albeit
>> much more slowly. What is sometimes left after a long period of weathering
>> is a pattern of parallel grooves on the outer surface that might be
>> (mis)interpreted as flow lines.
>>
>> This is an effect that I first noticed on a thick slice of Toluca from Alain
>> Carion's collection that was on display at a wonderful exhibition at the
>> Ecole des Mines in Paris in 1998. The correspondence between the shallow
>> ridges on the oxidized edge of the slice and the Widmanstaetten pattern of
>> the cut surface was rather obvious.
>>
>> There might be something about the specific soil chemistry at the site that
>> could make this effect more pronounced at some localities (e.g. Nantan or
>> Toluca) by enhancing the difference in oxidation rate.
>>
>> Piper
>>
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Received on Mon 28 Sep 2009 03:52:41 PM PDT