[meteorite-list] a question on fusion crust

From: Michael Farmer <meteoriteguy_at_meteoritecentral.com>
Date: Thu, 22 Mar 2007 09:14:20 -0700 (PDT)
Message-ID: <135501.73823.qm_at_web33107.mail.mud.yahoo.com>

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.
Thus, FUSION CRUST
It is quite obvious that the surface of a freshly
fallen iron, with the blue-black coating is a FUSION
CRUST.
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 of 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 12:14:20 PM PDT