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