[meteorite-list] Fusion Crust on Irons

From: MexicoDoug <MexicoDoug_at_meteoritecentral.com>
Date: Mon, 4 Dec 2006 14:16:56 -0500
Message-ID: <011701c717d8$c4d61e10$294d81ac_at_thedawning>

Hey Gary. No problem, that's my best answer but I'm sure others with other
points of view could add a lot of complementary information. I should have
mentioned, too, that the nice black magnetite that developes on the surfaces
of irons in meteorite-friendly desert environments is often called 'fusion
crust'. That is not exactly the same as the fresh stuff - that is more like
the desert varnish for an iron loosely said. The good thing about it is
that it serves to seal naturally in the rest of the meteorite by forming an
alread oxidized and thus inert protective skin. That's great to have anyway
and whether someone is over zealous to call it fusion crust or not. Too bad
it has to be cut to appreciate on small pieces.

In Marcin's case, though, he argues that you can see flow lines. This is
where it gets semantic. I'd just agree with him since he's absolutely right
that they were caused in the fusion even. But, I would temper (!) that with
the knowledge that they may be mineralized and compositionally just a
reminder of what they once were. Still, sounds superbe to have that on a
5000 year old iron meteorite, by any name!

Martin at Chladni Hairs have a beautiful Boguslavka Iron (a witnessed fall)
which has a thick melted skin, so it would be nice to hear from them about
how that fits into my limited try at this (maybe it was exposed to something
hot in space, ie got close to the Sun, and as Larry Lebovsky will be quick
to point out, radiative heating can be brutal and cause asteroid skins. I
just don't know how that could survive in tact throughout entry...

Best wishes, Doug

----- Original Message -----
From: "Gary K. Foote" <gary at webbers.com>
To: "MexicoDoug" <MexicoDoug at aim.com>; <meteorite-list at meteoritecentral.com>
Sent: Monday, December 04, 2006 2:03 PM
Subject: Re: [meteorite-list] Fusion Crust on Irons


> 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
>> >
>> > ______________________________________________
>> > Meteorite-list mailing list
>> > Meteorite-list at meteoritecentral.com
>> > http://six.pairlist.net/mailman/listinfo/meteorite-list
>> >
>>
>
>
>
>
Received on Mon 04 Dec 2006 02:16:56 PM PST