[meteorite-list] Gebel Kamil iron is official now - 1.6 metrictons!?!?

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Tue, 13 Jul 2010 11:06:17 -0700
Message-ID: <AANLkTik0KTUyihbaxEANE4kjUYEzurjRoaOuGSZ_JTSb_at_mail.gmail.com>

Martin,

I have two problems with what you're saying. Firstly, you're saying
that shrapnel doesn't exhibit a widmanstatten pattern in general.
Your base this claim on heat-altered Canyon Diablo 'rim' specimens.

I'd like to point out that we don't know whether or not there exist
any true pieces of shrapnel from the Canyon Diablo impact event. I
have seen heat-altered pieces of Canyon Diablo, but I have never seen
*shrapnel* pieces of Canyon Diablo (individuals/fragments are too
weathered to tell original surface features, and I have never seen a
piece of Canyon Diablo that displayed a mechanically distorted
pattern).

To be frank, I doubt that any true shrapnel exists from the event.
The energy released by the event was more than enough to simply melt
and vaporize the entire impactor.

Which is why I have a problem with your equating the Sikhote-Alin
impact event to the Canyon Diablo event.

I'm really surprised that you would call the two events similar - one
was a large scale vaporization event and the other was a simple
explosive event in which individuals shattered. They're really quite
different.

And yes, I know about Morasko and Seel?sgen shrapnel - both of which
*also* display a widmanstatten pattern when cut.
Thomasz sent me some excellent photos this morning, but I didn't feel
like getting them up to post to the list.
In retrospect, I recall that Marcin used to have some on his site:

http://www.polandmet.com/_seelasgen.htm

Wha-la.

So I've posted numerous photos of distorted (but existing)
widmanstatten patterns of cut shrapnel for you to look at, and yet you
seem set on insisting that shrapnel doesn't exhibit a widmanstatten
pattern!

"Well, for me - maybe I'm there conservative - a shrapnel is a totally
destroyed and tattered lump of an iron meteorite, which fully has lost its
original structure due to the forces of a major explosion."

To my knowledge, this sort of meteorite *does not exist.* Heat-altered
specimens of Canyon Diablo show no physical distortion (just a
watering-down of the pattern), suggesting that they are not shrapnel,
but that they are rather pieces of the meteorite that simply fell near
the crater itself as it was forming (and were thus exposed to the heat
released by the explosion). They do not appear to be explosively
ejected fragments as we see with Henbury and Sikhote-Alin. Such
fragments exhibit violently twisted patterns (see Henbury photo from
my last email).

So, with regards to your statement:
Seeing as there are no known low-nickel (meteorites that would
otherwise form a widmanstatten pattern) "ataxites" (meaning, in this
case, a widmanstatten-less iron, regardless of nickel content) related
to known impact events on earth, there likely exist no shrapnel
meteorites in the world, according to your definition.

And, yes, I suppose they might find pieces of this Egyptian meteorite
that exhibit a widmanstatten pattern.
This seems, however, to be highly unlikely, for three reasons:
1) This was a simple explosion event in which little vaporization and
thus general heating of the meteorite fragments took place. In other
words, this was a hell of a lot smaller than the Canyon Diablo event,
and is much more in line with a Sikhote-like event. As we can see
with Sikhotes, true shrapnels show violent signs of deformation and
compression, but no signs of pattern erasure due to impact. If you've
never seen an etched piece of Sikhote shrapnel in all your years of
dealing with meteorites, I really don't know what to say to you - I
couldn't find any good examples of photos online, but you must have
seen some in the past. I've seen many.
2) The only crater that we know of that has actually produced
heat-altered irons amongst a field of otherwise unaltered irons - is
Canyon Diablo. Seeing as the Henbury impact event was larger than
this one (the largest Henbury craters were larger than 40m) -- and the
specimens created were shrapnels with preserved widmanstatten patterns
-- we can draw a conclusion.
It's a smaller crater. Less kinetic energy was released in this
event, and if there wasn't enough released at Henbury to erase the
pattern contained within the shrapnel there, I think it's safe to
assume that the same didn't happen here.
3) You should also note that such a melting/reheating event would
significantly alter the pattern that we would see:

http://tin.er.usgs.gov/meteor/metbull.php?code=52031

A flash-reheating capable of erasing the meteorite's structure would
erase a plessitic pattern, FYI. It takes an extremely long period of
time for such crystals to form out of solidified Taenite, and they
could not form on earth.

In summation -

I disagree with your notion of shrapnel, because if I were to believe
it, I would have to say that meteoric shrapnel likely does not exist
on earth. I also find it highly unlikely that this 'Gebel Kamil'
exhibited a different widmanstatten pattern prior to impact because
the pattern that it exhibits could not have formed during or post
impact.

Regards,

Jason

On Tue, Jul 13, 2010 at 10:09 AM, Martin Altmann
<altmann at meteorite-martin.de> wrote:
> Hi Jason,
>
> well and the Sikhote-shrapnels?
> Or remember these Canyon Diablos, found on one side of the crater rim, where
> the pattern was completely annihilated by heat and which are completely
> recrystallized.
>
> If one would had only such examples of Canyon and Sikhote, undoubtedly they
> would be given the structural type: ataxite.
>
> (Btw. the Bavarian iron find Inningen, which still hasn't been removed from
> the Bulletin, which has identical values like Sikhote, got as structural
> type also ataxite, cause it was a shrapnel. ...a Sikhote-like shrapnel,
> havig the same trace element data like Sikhote and found without any other
> pieces nor any impact structures or pits lying on a road - ouch! That
> hurts...).
>
> All I'm telling is, that it might be too early to commit to that structural
> type with the Egypt iron, as maybe there will be still found (or examined)
> more intact pieces.
>
> Like so many in this thread I know Gebel Kamil only from the loads our
> Russian finder kings brought to light and to Ensisheim.
>
> They were all extremely stressed, sharp-edged, tattered and torn frazzles of
> iron - just like the shrapnels we all know from Sikhote-Alin.
>
> How distorted and stressed they are, you can observe on the extremely
> disturbed and deformed schreibersites in Mirko's slices, if you compare
> these to the large, angular skeletonised schreibersite crystals in
> Sikhote-individuals or in Guanaco e.g.
>
>
> You could add also Morasko to your list.
>
> Well, for me - maybe I'm there conservative - a shrapnel is a totally
> destroyed and tattered lump of an iron meteorite, which fully has lost its
> original structure due to the forces of a major explosion.
> I guess, that's why also the military term "shrapnel" was used as an
> analogue for this type of iron meteorites.
>
> Those which you mean, which show a partial deformation, I wouldn't call in
> my personal use "shrapnels", at best maybe partial shrapnels.
> But that depends on one's individual interpretation, I omit,
> because "shrapnel" is a not exactly defined term, similar as we have it with
> "orientation" or more recently with the "hammer stones".
>
> Best!
> Martin
>
>
>
>
>
>
>
>
> -----Urspr?ngliche Nachricht-----
> Von: meteorite-list-bounces at meteoritecentral.com
> [mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von Jason
> Utas
> Gesendet: Dienstag, 13. Juli 2010 15:23
> An: Meteorite-list
> Betreff: Re: [meteorite-list] Gebel Kamil iron is official now - 1.6
> metrictons!?!?
>
> Hello Mirko, All,
> That's just not true at all - plenty of irons have seen plastic
> deformation without becoming ataxites.
>
>
> Seymchan:
>
> http://www.carionmineraux.com/mineraux/Mineraux_Juillet_aout_2008/meteorite_
> seymchan_1.jpg
>
> http://www.imca.cc/insights/2007/II06-img/Seymchan.jpg
>
>
> Henbury:
>
> http://www.minresco.com/meteor/meimages/me606d.jpg
>
>
> Uruacu:
>
> http://cgi.ebay.com/LOW-PRICE-URUACU-IRON-METEORITE-BRAZIL-END-CUT-804-GMS-/
> 200446229790?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item2eab86bd1e#ht_1622w
> t_906
>
> http://cgi.ebay.com/LOW-PRICE-URUACU-IRON-METEORITE-BRAZIL-END-CUT-514-GMS-/
> 200421205241?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item2eaa08e4f9#ht_1579w
> t_906
>
>
> - I've also seen examples of similar features in Sikhote-Alin,
> Boxhole, Gibeon, and Campo del Cielo.
>
> Plastic deformation due to impact does not result in the complete loss
> of widmanstatten pattern. ?The only plastically deformed ataxites that
> lack any true pattern (that I can think of) are Chinga (deformed
> schlieren) and this new Egyptian iron, neither of which appear to have
> had widmanstatten patterns before entering the atmosphere.
>
> Regards,
> Jason
>
> On Tue, Jul 13, 2010 at 5:30 AM, Martin Altmann
> <altmann at meteorite-martin.de> wrote:
>> But is there a finest octahedrite among the chemical
> IAB/IIICD-complex....?
>> And are there coarsest octahedrites to be found among the IVAs?
>>
>> I think, it's quite reasonable, not to give a structural type at that
> point
>> of time for the Egypt iron, if there were only shrapnels found,
> respectively
>> analyzed.
>> Shrapnels by their nature are always ataxitic.
>>
>> Or was meanwhile a not so damaged individual found and examined?
>>
>> Best!
>> Martin
>>
>>
>> -----Urspr?ngliche Nachricht-----
>> Von: meteorite-list-bounces at meteoritecentral.com
>> [mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von Jeff
>> Grossman
>> Gesendet: Dienstag, 13. Juli 2010 13:48
>> An: meteorite-list at meteoritecentral.com
>> Betreff: Re: [meteorite-list] Gebel Kamil iron is official now - 1.6
> metric
>> tons!?!?
>>
>> "Ataxite" is a structural term, like octahedrite and hexahedrite.
>> Modern classification of iron meteorites is based on the chemical group,
>> which can tell you something about the parent asteroid. ?The structural
>> classification is quasi-independent of the chemical classification,
>> inasmuch as members of each structural group can belong to multiple
>> chemical groups. ?So "ataxite" has not been replaced with "iron,
>> ungrouped." ?Both are correct.
>>
>> When I used to edit MetBull, the heading on the description of this
>> meteorite would have said "Iron, ataxite (ungrouped)", but other editors
>> have abandoned this.
>>
>> Jeff
>>
>>
>>
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Received on Tue 13 Jul 2010 02:06:17 PM PDT