[meteorite-list] a question on fusion crust

From: MexicoDoug <MexicoDoug_at_meteoritecentral.com>
Date: Thu, 22 Mar 2007 12:06:44 -0600
Message-ID: <006801c76cac$dbd20f60$b5ce5ec8_at_0019110394>

Mike wrote:
"Crust is crust, soft, hard, it doesnt matter."
Definitely agree. There is no need to create new definitions just because
we are more familiar with stony fusion crusts than we are with iron fusion
crusts.

"It is a crust of material caused to be on the surface of the object by
fusion."

Not exactly in agreement since there are ways to get crust without fusion,
but still it is fine because while fusion isn't the whole story it is
definitely the underlying story for fusion crust formation in iron
meteorites. So I would just say caused "during" fusion, but this difference
is inconsequential except for this debate to define carefully what we are
talking about.

Elton's argument that Vagn Buchwald probably would NOT have called "fusion
crust" on iron meteorites "fusion crust" if he thought about it seems to be
behind this whole argument. Let me stipulate that Vagn Buchwald wouldn't
call iron meteorites, "meteorites", if he though about it and the scientific
community recognized the term "sky slag" instead. (They look different from
stony meteorites inb many ways - so what). That didn't stop him from
writing the "Handbook of Iron Meteorites" with sections on "fusion crust"
and its scientific study. Since few people have seen good examples of
fusion crust on irons, I think at issue also is the fact that it is
unfamiliar that is causing some of the desire to improperly discriminate
between the two terms. This is about as fun as the Pluto planet debate.
The terms are out there in the literature. If Elton wants to revise the
scientific literature and gets scientific peer agreement, no problem. But
at the moment having the conversation suggesting that collectors change
their definition is fruitless on the meteorite list except for its
educational value about the composition of fusion crusts, and pleasue of the
sport of debate.

Best Health,
Doug




> Why would iron fusion crut not be different than that
> of stones? Of course it is chemically different. You
> know, you can remove the fusion crust on some stones
> easily as well, so what if most of the crust on irons
> is softer, and can fake off easily. The subsurface is
> smooth, and much more difficult for the crust to
> adhere to.
> Go to Vienna and check out Cabin Creek, 100%
> blue-black fusion crust on the most beautiful iron
> fall I have ever seen. It is not rust, nothing but a
> crust caused by intense burning in the atmosphere.
> You can debate over the chemical composition of the
> heat altered layer on the surface of irons all you
> want, but it is fusion crust.
>
> Michael Farmer
>
>
> --- Armando Afonso <armandoafonso at oniduo.pt> wrote:
>
> > In that case, you get a vitrification of the
> > silicates, with some inclusion
> > of reduced iron, eventually coming from the
> > pyroxenes or olivine, giving it
> > the dark tone.
> > Anyway, we are really speaking of diferent and new
> > minerals.
> > Normally that crust is harder than the meteorite in
> > itself.
> > AA
> >
> > ----- Original Message -----
> > From: "Michael Farmer" <meteoriteguy at yahoo.com>
> > To: "Armando Afonso" <armandoafonso at oniduo.pt>;
> > <meteorite-list at meteoritecentral.com>
> > Sent: Thursday, March 22, 2007 4:48 PM
> > Subject: Re: [meteorite-list] a question on fusion
> > crust
> >
> >
> > > But made from the matrix component. burned
> > material
> > > from the parent body, regardless of how it is
> > > chemically changed, same as the fusion crust on
> > any
> > > meteorite. Take a Eucrite like Stannern for
> > example,
> > > white interior, yet the fusion crust is glossy
> > black.
> > > That is not soot, it is chemically altered matrix.
> > > Nothing more.
> > > Michael Farmer
> > > --- Armando Afonso <armandoafonso at oniduo.pt>
> > wrote:
> > >
> > >> 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.
> > >> AA
> > >>
> > >>
> > >> ----- 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.
> > >> > 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
> > >> > .
> > >> > 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.
> >
> === message truncated ===
>
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Received on Thu 22 Mar 2007 02:06:44 PM PDT