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

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Mon, 28 Sep 2009 12:55:52 -0700
Message-ID: <93aaac890909281255i1609db97vdbc317731e90a508_at_mail.gmail.com>

Hello Guido, Piper, Mike, All,
Ah, excellent clarification - makes a lot more sense, but -
I'd still have to say that any lines on the "surface" of the iron
would be artifacts of the corrosive process or of your cleaning of the
iron. I put surface in quotes, because, as has already been stated,
after cleaning an iron like a Nantan, what you're looking at
originated likely more than a few centimeters below the original
surface of the meteorite.
If you could take some pictures, I'd be curious to see..
Thanks, Regards,
Jason

On Mon, Sep 28, 2009 at 12:52 PM, <countdeiro at earthlink.net> wrote:
> 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 03:55:52 PM PDT