[meteorite-list] Fusion Crust on Irons

From: Mike Fowler <mqfowler_at_meteoritecentral.com>
Date: Thu, 7 Dec 2006 14:49:35 -0600
Message-ID: <A1AD5F76-B530-4992-8F94-6EA52F4D2F94_at_mac.com>

Hi Jason,

Thanks for your thorough and I might say persuasive commentary on
fusion crusted irons. I did note one possible discordant data.
Campo del Cielo is an approximately 5000 year old fall and Nantan is
500 years old. Is the Nantan region so much worse (wetter?) that no
fusion crust can be found?

Also, how about the main mass of Taza? Does that have crust? If you
want to share more pictures, it would be greatly appreciated.

Thanks,

Mike Fowler
Chicago
ebay--starsandrocks

> Hello All,
>
> Might be a little on the tail end of this thread, but I think it still
> merits posting...
>
> Although there may be exceptions where an iron lacks fusion crust
> do to a
> late atmospheric breakup or weathering, as might any stony
> meteorite, they
> do, in general, possess just such a skin after having fallen to the
> earth.
>
> However, many peoples' opinions of what exactly this crust consists of
> differs greatly with regard to irons. I've seen many a Canyon
> Diablo or
> Campo regarded as possessing fusion crust, when there is truly none
> of the
> remaining original surface left, and mm if not cm of material have
> corroded
> off of the surface since the fall.
> That being said, the same argument applies to stony meteorites.
>
> Are any Canyon Diablo's truly crusted? I can very safely assume
> that no,
> none of them was picked up after the fall and stored away in some
> humidity
> controlled pueblo, to be rediscovered some 50,000 years later. In just
> about every case, they've lost several mm if not a few cm (some large
> specimens have rusted clear though) off of every surface, so though
> they
> could, and should, be deemed complete individuals, they are in no way,
> shape, or form, crusted.
>
> Campo Del Cielo....
> Firstly, what an amazing fall. Large beautiful irons in such an
> abundance
> as to flood the market in every sense of the term.
> That being said, many do have a tendency to rust. And many have
> corroded to
> the point of looking like rather abstract iron potatoes or larger
> lumps,
> possessing little semblance of their original flight-marked forms,
> all of
> these traces having been removed by weathering eons ago.
> However, on many of the 'new Campos' of several years ago, one can
> find
> patches of fusion crust with ripples and flow lines (and even a few
> impact
> pits). Could this really be deemed fusion crust?
> I think so. When cut, many of the irons show a heat rim that clearly
> display the fact that at least some of them have not lost much, if
> any of
> their original surface. These patches are oftentimes small, but we
> do have
> one in our collection that we purchased a number of years ago that
> is a
> spectacularly oriented specimen which is visually comparable to many
> Sikhote-Alins, with a full side of blue-black ripples and spatters.
> The
> back is glypted, and displays much crust as well.
> Here's an image of the leading edge of the specimen:
>
> http://i50.photobucket.com/albums/f306/JUtas/meteorites/P1010040.jpg
> (It's concave - hence the lack of flowlines and rippled appearance.)
>
> And the trailing edge with it's fusion crusted glypts:
>
> http://i50.photobucket.com/albums/f306/JUtas/meteorites/P1010043.jpg
>
> For another example of this, I believe Matteo could provide us with a
> picture or two of one of his newer Campos...he posted some a while
> back, and
> they showed a very fresh-looking iron.
>
> Onto Morasko...
> Well, firstly, who ever said that it fell ~5,000 years ago?
> Firstly, I can
> quote Buchwald as saying in his catalogue of iron meteorites, that
> "Fusion
> crusts may be detected in numerous places." The assumption that it
> is a
> glacially transported meteorite is also completely false, seeing as
> there
> are craters nearby in which specimens have actually been found that
> have
> been dated to roughly the same age as the fall itself.
> For photos, I'd simply go to Marcin, as he's already put some up
> for the
> more suspicious parties. It's fusion crust in those pics, you can
> be sure.
> I've seen another ~70kg individual recently myself, and am certain
> that it
> has large areas of crust.
>
> Regarding Sikhote Alin, one must tread carefully. Many individuals
> being
> found today are cleaned using ball bearings (tumbling), which,
> although they
> give the irons a pretty shine, removes much of the fusion crust. In
> fact,
> if your Sikhote's have a shiny, rather than matte look to them,
> they may
> still have some crust, but you've lost at least the majority of its
> thickness. Here are a few pics to show the basic differences
> between the
> two.
> Tumbled, with assiciated sheen:
>
> http://i50.photobucket.com/albums/f306/JUtas/meteorites/DSCN1077.jpg
>
> Cleaned using some other method:
>
> http://i50.photobucket.com/albums/f306/JUtas/meteorites/DSCN1091.jpg
>
> There's a clear difference between the two; on one, the flowlines have
> nearly disappeared altogether whereas the other even possesses some
> of its
> original compression waves formed by varying degrees of heat and
> compression
> on the leading edge of the iron.
> Is this fusion crust?
> Well, it's melted and was at some point flowing. It may not be the
> topmost
> layer of crust, but it's certainly fusion crust, of that there can
> be no
> doubt.
>
> In general...old falls like Odessa, CD, and Nantan will, I can
> promise you,
> never show any trace of crust ever (well, oxide, but that's another
> issue).
> As for others such as Henbury or Campo Del Cielo....well, I've seen
> some
> nice Campo's and some really nicely oriented Henburys....
> Sikhote's are, of course, fusion crusted, at least if they're
> individuals
> and aren't too weathered. And if they're not individuals, hell,
> they're all
> the more rare - how many falls in modern times have produced any
> amount of
> iron shrapnel?
> -Two...Sikhote and Sterlitamak, only one of which is readily
> available to
> collectors.
>
> Anyone have any other common (or uncommon) irons to put forth?
>
> Regards,
> Jason
Received on Thu 07 Dec 2006 03:49:35 PM PST