[meteorite-list] Fusion Crust on Irons was AD- Coins etc.

From: Martin Altmann <altmann_at_meteoritecentral.com>
Date: Tue, 5 Dec 2006 02:22:09 +0100
Message-ID: <012d01c7180b$c97fc7d0$4f41fea9_at_name86d88d87e2>

Oh, I don't think, that no fusion crust is possible on iron meteorites at
all, but I wanted to exclude, that on such an stone-old iron like Morasko,
could be fusion crust found.

Boguslavka - one piece was found directly on the day of the fall, the other
piece was recovered very soon later. So I think these dark layer with the
little flow lines is true fusion crust, as the iron had no chance to be
modified by weathering.

Helpful in this respect was also the pictured Sikhote-Alin, where I send a
link too. It was from a museum, absolutely pristine and uncleaned most
probably from the first expditions from uncle Krinov.
And it has a fusion crust! Not any blue haze of a few dozen micrometer as
Norton writes, but rather a fusion crust a little less thick than a
fingernail. Btw. missing in prominent edges. The crust hadn't it's original
colour, a little bit oxidized to ochre.

Small patches from such a kind of crust I found sparsly on a dozens or so
"modern" Sikhotes out of thousands, which weren't so over-cleaned like most
of the material, which nowadays is around. Most suppliers are selling
tumbled, brushed ect. Sikhotes - I mean nowadays in as-found-condition they
wouldn't be quite pretty - perhaps Ican can supply us with some pics.
Those patches survived in regmaglyptes, sometimes showing concenting flow
marks.

With the famous blueish tint I'm a little bit at a loss.
I found it from time to time on more carefully cleaned Sikhotes.
(That they would artificially heated I exclude, if you remember, the
Russians liked to oil their little specimens with a black and tough grease -
so why the should have made them blue before?).
That blueish tint must be indeed a very thin layer, easily to destroy while
cleaning.
Btw. I never saw a blue Sikhote-shrapnel.

There I remember that fresh iron Hmani had 3 years ago in Munich, it was
such a blue iridescent blue one.
And sometimes one can see it at the rust free parts of Taza.

Back to fat crust - on Udei Station I found some parts of a fat black crust,
Lowicz, the mesosiderite, has a good black fusion crust...

Well - a reheated rim is no indicator for a fusion crust, but where no
reheated rim, there no fusion crust left, I'd say.

Guanaco has a fine recrystallized rim and I guess on one side also a little
crust, perhaps a fusion crust.

Sooo - I'm no chemo-physicist, that's why I asked here on the list, so I
have no idea, which mechanism could replace a fusion crust of younger iron
falls and how to discern oxidation by fusion from erosion by weathering,

But I refuse to believe, that such a thin and delicate fusion crust, thinner
than 1mm, on a chunk of solid iron, could survive hundreds and thousands of
years of terrestrial oxidation.

For me don't exist fusion crusted Gibeons, Nantans, Brahins, Campos,
Henburies, Mundrabillas and so on.

And especially not with a Morasko, sitting in the moisture in a wet climate
for thousands of years, especially not if it was thrown in acid to derust
it.

Well, I haven't munched the wisdom by spoon - (I don't make a great show of
learning). Perhaps some one will enlight me?

Yep - to sell desert varnish on stones as fusion crust is very popular on
ebay.
   
Buckleboo!
Martin

PS:
http://cgi.ebay.com/19-8-kgs-NEW-CAMPO-DEL-CIELO-METEORITE-HUGE-46-pounds_W0
QQitemZ120057887354QQihZ002QQcategoryZ3239QQrdZ1QQcmdZViewItem

That's also such a hero! Where the heck on his hundreds of Campos should be
there fusion crust? They are freshly cleaned..ouch!

-----Urspr?ngliche Nachricht-----
Von: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von Mr EMan
Gesendet: Dienstag, 5. Dezember 2006 01:06
An: Martin Altmann; meteorite-list at meteoritecentral.com
Betreff: Re: [meteorite-list] Fusion Crust on Irons was AD- Coins etc.

I am in agreement with Martin. This is a myth that we
shouldn't allow to perpetuate on the list. An
Iron/siderite my have an original ablation surface, as
well as flow characteristics but won't have a "fusion
crust". There are many reasons I won't go into about
why iron doesn't have the composition to glass up. It
can and does develop a film of carbon and magnetite
owing to combination with atmospheric oxygen.

 I think the phrase fusion crust has been repeated so
often people have no idea what it really is. A freshly
fallen iron may have a film or veneer that you can
wipe off--but not a crust! So on this Norton and I
disagree on semantics.

As a side to all the claims of fusion crust on these
sand blasted NWA's on Ebay --"t'ain't so neither". The
glass froth we know as fusion crust is gone. Fusion
crust is easily worn away on exposed surfaces and
easily etched when in contact with the soil. What
remains is unmelted scorched matrix devoid of fusion
crust.


In the midst of this writing I see there is a healthy
debate raging on the list. I'll post now and read
later.

Elton

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Received on Mon 04 Dec 2006 08:22:09 PM PST