[meteorite-list] Fusion Crust on Irons

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Wed, 6 Dec 2006 18:38:26 -0800
Message-ID: <93aaac890612061838t39c254b7ob16743b8d0201bf_at_mail.gmail.com>

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


On 12/4/06, Gary K. Foote <gary at webbers.com> wrote:
>
> I have a number of sikhotes that have that nice blue sheen. Beautiful for
> sure.
>
> Gary
>
> On 4 Dec 2006 at 12:10, Dave Freeman mjwy wrote:
>
> >
> > Get a fresh looking blue tinted shikote alin, now that is a fushion
> crust, about .0008
> > thick but still a fine crust of blue steel. Dave F
> >
> > Gary K. Foote wrote:
> > Thanks for clearing that up Doug. I've always felt a bit dumb
> talking about fusion
> > crust and irons.
> >
> > Gary
> >
> > On 4 Dec 2006 at 13:59, MexicoDoug wrote:
> >
> >
> > Hi Gary,
> >
> > Fusion crust can be in the eyes of the beholder, so the difficulty
> with this
> > question is we are making a one-size fits all definition.
> >
> > For the irons, you could get a verrrry thin local destruction of any
> > crystalline patterns or figures (no longer etch), some chemical
> change from
> > 'burning' up including colors. In the case of stones, it is a
> different and
> > typically a glazed-silicate ceramic crust forms. It can get a
> rainbowish
> > tint from burnishing, though it usually looks somewhat bluish. It's
> so thin
> > that it quickly is lost to other mineralization in the oxidizing
> humid
> > environment that is earth's.
> >
> > So there is a difference. But loosely thay can all be attributed to
> > 'fusion' though in the case of iron it has a different
> characteristic. In
> > either case, when the fusion crust is black, this is generally
> caused by
> > oxidized iron during the entry, not terrestrialization. That is a
> main
> > difference between what we see on many older irons in dry and stable
>
> > environments.
> >
> > So, yes, irons can have a fusion crust, it is just not predominantly
> a
> > ceramic kiln glaze best seen from some achondrites, which is the
> classic...
> >
> > Best wishes, Doug
> >
> >
> > ----- Original Message -----
> > From: "Gary K. Foote" <gary at webbers.com >
> > To: < Meteorite-list at meteoritecentral.com>
> > Sent: Monday, December 04, 2006 1:26 PM
> > Subject: [meteorite-list] Fusion Crust on Irons
> >
> >
> >
> > Hi All,
> >
> > Recently I have read a few posts to this list that definitively
> claim that
> > irons do not form a fusion crust. Yet, in Norton's "Rocks From
> Space",
> > [pg 167 in my softbound edition] it clearly states the following;
> >
> > "Iron meteorites have the thinnest crust of all, usually only a
> small
> > fraction of a millimeter thick. A fresh crust is blue-black to
> black and
> > looks like freshly welded steel. This crust is fragile and easily
> > destroyed if the meteorite weathers for even a short time."
> >
> > So, which is true? Crust or no crust for irons?
> >
> > Gary Foote
> > http://www.meteorite-dealers.com
> >
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> >
> >
> >
> >
> >
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>
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Received on Wed 06 Dec 2006 09:38:26 PM PST