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, <[email protected]> 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 <[email protected]> >>Sent: Sep 28, 2009 4:45 AM >>To: Meteorite-list <[email protected]> >>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 <[email protected]> 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 >>> >>> ______________________________________________ >>> http://www.meteoritecentral.com >>> Meteorite-list mailing list >>> [email protected] >>> http://six.pairlist.net/mailman/listinfo/meteorite-list >>> >>______________________________________________ >>http://www.meteoritecentral.com >>Meteorite-list mailing list >>[email protected] >>http://six.pairlist.net/mailman/listinfo/meteorite-list > > ______________________________________________ http://www.meteoritecentral.com Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
