[meteorite-list] a question on fusion crust

From: Armando Afonso <armandoafonso_at_meteoritecentral.com>
Date: Thu, 22 Mar 2007 16:31:56 -0000
Message-ID: <002301c76c9f$9bd843f0$62b0fea9_at_TOSHIBA>

Obviously, it is a diferent material...
The external fusion crust of iron meteorites is Magnetite, the result of the
combination with the air`s oxygene.

----- Original Message -----
From: "Michael Farmer" <meteoriteguy at yahoo.com>
To: "Mr EMan" <mstreman53 at yahoo.com>; "Michael Murray"
<mmurray at montrose.net>; <Meteorite-list at meteoritecentral.com>
Sent: Thursday, March 22, 2007 4:14 PM
Subject: Re: [meteorite-list] a question on fusion crust

> This is simple.
> Fusion, the result of material burning at extreme
> temeratures, and crust, the layer on the surface that
> was not there before re-entry.
> It is quite obvious that the surface of a freshly
> fallen iron, with the blue-black coating is a FUSION
> It generally can't be "wiped" off. I have pieces in my
> collection, Bugoslava for example, with a .5 mm layer
> of blue-black fusion crust, that survived cutting and
> polishing of the meteorite, so it is not exacly
> "soot". Of course the crust is the same as the parent
> material, even on stones. How could it be of a
> different material? How could an object, falling
> through the atmosphere, get coated with anything but
> it's own matrix as it burns? Yes, the silicates can be
> altered due to heating, while irons tend not to
> chemically alter.
> Elton, I think you are about the only one in the world
> that thinks fresh fallen iron meteorites do not have
> fusion crust.
> Michael Farmer
> --- Mr EMan <mstreman53 at yahoo.com> wrote:
>> The "soot" coating you are talking about is mostly
>> freshly created magnetite (micro /nano crystals)
>> from
>> the oxidation of iron whilst passing through the
>> incandescent phase. It adheres by magnetism and can
>> be wiped off with rough handling. There is probably
>> a
>> carbon component however graphite turns to carbon
>> dioxide upon burning >
>> There are several other terms for the zone
>> associated
>> with "ablation" heating, one of which is in the
>> literature: "zone of thermal alteration". When there
>> is an oxidation coat
> .
> native elements such as
>> found
>> on sodium or phosphorus it is sometimes called a
>> rind.
>> This is what I favor to describe the coatings on
>> irons--the one before terrestrial oxidation also
>> known
>> as rust.
>> In my view there can be no crust when the chemical
>> and
>> physical characteristics of the surface do not
>> differ
>> from the donor material. That lets the door open
>> for
>> irons having crust and at least most agree that it
>> is
>> unlike the fusion crust of stoney meteorites.
>> While at the Smithsonian inspecting the collection
>> up
>> close and personally, I was advised to use caution
>> in
>> examining a fresh iron as the coating would rub off
>> easily. They didn't call it fusion crust but the
>> issue
>> never came up. The point being, not everyone is in
>> agreement nor is there universal usage.
>> Critical analysis on the assumptions about fusion
>> crust on irons would likely lead to a more
>> descriptive
>> table of composition and relate that to the
>> metallurgy
>> and chemical composition of the meteorite itself. In
>> fact I believe research on crustal petrology would
>> be
>> reveling for all types of meteorites. I yet wonder
>> why
>> some lunarites have a brown bubbly crust. The crust
>> of
>> a iron meteorite on Mars will be different from one
>> here and I'd like to know what to expect and why.
>> Intuitively, I know there would be rare minerals
>> such
>> as nickel oxides,nitrates, phosphates perhaps even
>> a
>> sulphide and yes even O3 and O4 silicates. However
>> current wisdom is that crust is crust ego no
>> research
>> needs to be contemplated-NOT.
>> Some of the oft quoted god status experts who write
>> of
>> fusion crust on irons monitor this list and have
>> remained curiously silent on the topic. I hope this
>> topic is thought provoking for all parties.
>> I suppose that the use of the term "fusion crust"
>> universally with respect to irons is acceptable if
>> one
>> doesn't have a need for technical accuracy. One
>> thing
>> yet to be refuted here on the list is that the
>> "crust"
>> on irons is not composed of "glass".
>> Elton
>> --- Michael Murray <mmurray at montrose.net> wrote:
>> > Hi List,
>> > Are you ready for a dumb question! Here goes...
>> Is
>> > there a more definitive description of the
>> blackened outer layer on the surface of iron
>> meteorites than simply referring to it as "fusion
>> crust"? From what I can gather looking at different
>> pictures of stonys, they seem to have a glassy or
>> melted layer of the material of the stone. I can
>> see
>> that being a 'crust'. On at least some irons, there
>> is a coating but it doesn't appear glassy, just
>> blackened. I'm guessing that that coating is
>> partially resulting from burning of the gases in the
>> atmosphere? If it is a 'crust', it is not much of
>> one. It looks
>> like a very thin coating of soot that is adhered to
>> the stone, although more durable than soot. This
>> is
>> probably one of those dumb questions that the
>> Collection of Wisdom would answer.
>> The stone in this picture has the blackened layer
>> I'm referring to:
> <http://i127.photobucket.com/albums/p124/mmurray_02/IMG_0319.jpg>
>> Michael Murray
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Received on Thu 22 Mar 2007 12:31:56 PM PDT

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