[meteorite-list] Ablation Zone 5 Layers...Not

From: al mitt <almitt_at_meteoritecentral.com>
Date: Fri, 20 Nov 2009 11:45:20 -0500
Message-ID: <D611957409DA4FA8A0C7DF918B18D938_at_StarmanPC>

Hi Elton,

You've brought up some very good discussion on the definition of fusion
crusted specimens. I went to the authority, Buchwald's Iron Meteorites to
see what he called it. He has written a lot about it. He states: "Cuts
perpendicular to the surface of a freshly fallen iron meteorite disclose
fusion crusts and heat affected rim zones. While the fusion crusts on stone
meteorites are usually a product of simple melting, the crusts on iron
meteorites are complex. The fusion crusts are the adhering remnants of
ablated metal from the last part of the trajectory left on the surface when
the velocity decreased below about 3 km/sec., and ablation ceased. The
fusion crusts are, in principle, composed of an exterior fully oxidized,
rapidly solidified nonmetallic melt."

He shows a number of samples that are iron meteorites with various fusion
crusts and identifies them that way. In some cases thick metallic fusion
crust to describe flows and so forth. While I think there is some agreement
with what Buchwald said and your trying to say, he still calls it fusion
crust. Not to say that it is a term that is accurately describing a
scientific effect on the outside of iron specimens.

I have always felt and called some of my fresh iron falls fusion crusted
because that is what Buchwald has defined them as in his books and feel it
is a fair term to use unless a better term is identified and used by the
scientific community that would label it different. I do know as you have
pointed out that the term is often exaggerated way beyond the term that
accurately defines it in Buchwald's Books and certainly abused by some
seller of meteorites. Perhaps with this discussion, the overuse of the term
on irons will be more carefully applied. All my best!

--AL Mitterling

Mitterling Meteorites


----- Original Message -----
From: "MEM" <mstreman53 at yahoo.com>
To: "Meteorite-list" <meteorite-list at meteoritecentral.com>; "Jason Utas"
<meteoritekid at gmail.com>
Sent: Friday, November 20, 2009 9:01 AM
Subject: Re: [meteorite-list] Ablation Zone 5 Layers...Not


Dear Jason If everything is a part of the fusion crust than every meteorite
is fusion crusted end of discussion. So are you really saying that every
meteorite regardless of how condition has fusion crust even if all the extra
trans-located material is missing?

I don't have the luxury of going point by point as you have but apparently
you are unfamiliar with the Oxford and Cambridge dictionary definitions as
well as all their Dictionaries of Geology. Most of the literature and
practically all of the referenced websites use the silicate glassy/glassy
term in defining fusion crust--and in context they are most always speaking
of stoney meteorites.

 We've been down this discussion before and while I respect Buchwald's
observations: he is an industrial metallurgist and had no training I can
see in mineralogy nor geology. He became a iron meteorite subject matter
expert in his own right( I don't know that he ever did any work on any other
type. I see no incentive on his part to reevaluate the surface changes as he
was focused on cataloging the interior features. Somehow I don't think
"crust" was an issue for him and in the absence of inquiry into the use of
the term there was never a need to rethink it. He has an email
address--write him and ask him what he meant.

Nininiger was a biology teacher and while another legitimate self-made
expert in the field it wasn't technically oriented until late in his career.
This shouldn't be taken as disrespectful and doesn't mean that everything he
assumed was gospel-- especially given the state of scientific tools in his
lifetime. He laid the foundation for meteoritical study but that doesn't
mean he knew all there was to know about meteorites. His book about
meteorite surface features was mainly a photo documentation with little
analysis and generally lacking in comparative studies of the crust.

Much of this argument that they are "the experts" and as such are
infallible, is misguided and out of context, as the tools available now are
vastly more quantitative than tools of their day. So is our body of
knowledge more complete than during their careers. (

I am calling the ablation surface below any "crust" feature because
well...it is. The ablation surface is the last level we can ascertain the
fusion has occurred. When the crust is worn away the ablation surface is
revealed. I am also not calling the oxide coating a "fusion crust"
because,... well...it isn't ( necessarily) fused material and represents
either condensation or contact metamorphism of the final flight air soaked,
modified surface. I am also not calling the surface of SA's which show
aero-thermo-dynamic interaction that form the troughs "crust" because
partial melting/softening/gas jet ablation does not meet the definition of
fusion/fusing. How you see it as fusion crust illustrates my point that we
call everything fusion crust when it is not even fused material. I think it
deserves a more objective review and understanding of the complexities and
not reduced to a universal simplicity. As to my point about extensively
rusted/shalely Canyon
 Diablos being said to have "fusion crust", sounds like we are in violent
agreement.

The point of addressing the loss of the coating over time was to suggest
further inquiry into what the actual chemical composition was and to
indicate I felt it was a class of mineral/compounds which were unstable in
an oxygen rich atmosphere.

Again --some irons have apparent classical fusion crust but, I have to
disagree that all irons have fusion crust--that is why ablation surface is
an important distinction and is better nomenclature that serves as a
starting point for discussing all meteorite surfaces and where crust begins
and ends. I believe when and where it is found it needs as much analytical
scrutiny as we spend on the interior so we know its source material and how
it came to be crust.

Rather than me reiterate what I've already addressed perhaps you would like
to read it more collaboratively as some of what you replied to skipped over
where there is agreement and also you've challenged the studies about how
deeply thermal alteration occurs in different meteorites.

I am not ready to roll over on the claim that a chemically bonded oxide
constitutes fusion crust unless you want to drop the word fusion. I
proposed some terms for use in defining a meteorite's surface more
descriptively. Other than disagree out of principle, you didn't give a
counter argument as to why the model I laid out was in error.

Finally I will reiterate the problems with trying to have a reasonable
succinct discussion when out of context examples are introduced as if they
were the rule rather than the exception they are.

Elton

--- On Fri, 11/20/09, Jason Utas <meteoritekid at gmail.com> wrote:

> From: Jason Utas <meteoritekid at gmail.com>
> Subject: Re: [meteorite-list] Ablation Zone 5 Layers...Not
> To: "Meteorite-list" <meteorite-list at meteoritecentral.com>
> Date: Friday, November 20, 2009, 6:58 AM
> Hello Elton, All,
> I'm going to go through this bit by bit to do it
> justice...
>
>
> > Yes on a freshly recovered iron, there appears to be a
> "film" of what we believe is "magnetite-like oxide/nitride
> micro-crystals, probably including some sulfide and
> phosphide minerals" which form through interaction with hot
> atmospheric plasma. Even though some of it is magnetic,
> some of it is easily dislodged with a wipe of the finger.
>
>
> I assume this coating is relatable to the iridescent film
> which often coats stony meteorites - the film that often disappears
> within days of a fall.
>
> >I surmise that this rapidly goes to hematite or
> limonite but I've not thought through the chemistry and I
> suspect a valence discrepancy that makes this type meteoric
> "magnetite" unstable. The mineral assemblage in the
> coating/film is a result of passage through the atmosphere
> and not per se the resulting changes that occur with the
> passage of time on the surface.
>
>
> I shall point you toward this photograph of the external
> surface of a Sikhote-Alin. This iron was found ~50+ years after
> falling and still retained its exterior surface. The features you see
> are not made of melted Fe, but of an outer coating of iron oxide which
> formed during atmospheric descent.
>
> http://www.flickr.com/photos/cameteoritefinder/2335664239/sizes/l/
>
>
> > I think I can proffer an argument for what is and is
> not a scientifically underpinned definition of "crust" but
> I'll work on that later. For the time being the use of
> "crust" by present definition involves glass and last time I
> checked there is no such thing as "iron glass".
>
>
> Where did you get this definition? Why is it more
> valid than the one
> accepted by Buchwald, Nininger, Krinov, and the folks at
> the USNM?
> Why does fusion crust *have* to have glass in it?
> Honestly, this
> whole thing seems like a semantics battle on your part.
>
>
> >We expect to find something analogous to "crust" so we
> call what we see "crust"-- I understand that. But when we
> stray too far everything including dust mites, rust and,
> fungus gets called fusion crust.
>
>
> Right.
> Here:
>
> http://www.aerolite.org/catalogue/sikhote-alin-aaa-33-2.htm
>
> What you're looking at is the original external surface of
> the iron, made of that FeO layer that you keep insisting isn't fusion
> crust.It's perfectly analogous to the crust of stony meteorites,
> except, of course, in that it contains no glass.
>
>
> > As there is also a surface bluing occasionally
> observed (much like after welding) this may be a directly
> formed oxide/nitride layer of chemically altered meteorite
> while emerging from the incandescent phase of flight but
> since I am unsure of the composition I'll leave it out of
> the below discussion.
>
>
> I've seen that on stony meteorites as well. But since
> you're leaving it out, there's no real need to address it.
>
>
> > Chances are it is also quickly lost to weathering on
> the surface--even in the museum drawer.
>
>
> Maybe. I saw some pretty Oum Dreyga's with such a
> film still present as of this winter - in a drawer in Alain Carion's shop
> in Paris. As such, I have the feeling that such layers may not simply
> sublimate with time, but they do seem to disappear rather rapidly
> when meteorites are left in the field.
>
>
> >The bottom line here is: we have to accept the
> probability of an ever-evolving surface on our meteorites.
> Some happen quickly and may be gone in a flash and some oh
> so slowly. This should not deter us however from discussing
> the basis for each step that comes and goes.
>
>
> This also has nothing to do with our argument, for the most
> part. I don't think there's anyone here who denies such a fact, so
> stating it is somewhat superfluous.
>
> > I believe to discuss meteorite surface features e.g
> crust, non crust, flow lines, ripples, regmaglypts, pits,
> bubbles, and all the variations, we should come to a working
> definition in general principle of what to call them so we
> know we are discussing the same thing.
>
>
> Sounds good to me.
>
>
> > Part of that is acceptance that there is an
> "ablation/ablated zone" generally 2-6mm from the physical
> surface where the meteoroid last interacted with the heat of
> reentry. This zone my eventually be proved a new type of
> "rind", geologically speaking.
>
>
> Unfortunately, it's hard to gauge whether or not such a
> feature truly
> exists on stony meteorites because, due to their decreased
> conductivity, this heating does not occur over distances
> quite so large.
>
> See page two.
>
> http://adsabs.harvard.edu/full/1982Metic..17...27R
>
> So there's kind of an "ablationary rind," but it really
> only exists to the extent that you just noted in iron meteorites...
>
> Of the layers physically present, I see two
> branches/variations which we may reintegrate but for ease of
> discussion the first is mostly the non-silicate bearing iron
> branch of "layers":
>
> So we *are* talking about irons' fusion crusts...ok...
>
> > The ablated/ablation zone includes amongst it layers:
>
> > 1)Lost Layer/ Null layer: The material which is
> missing, includes ALL the material which is no longer there
> which we may conclude was lost from its pre-entry form due
> to atmospheric interaction. It may be marginal but may be
> needed to discuss surface depth in relation to cosmic ray
> tracks 14C concentrations, etc.
>
> O...k....the stuff that's no longer there. A wordy
> description, but
> sure. Call it what you will.
>
> > 2) Oxide Film or Coating: There is a layer of
> non-physically/non-chemically, bonded oxide film which is
> not persistent, subject to rapid erosion/weathering,
> abrasion etc. This represents a condensation coating which
> is applied after ablation stops. (See bluing discussion
> also)
>
> Such a coating forms on irons and stones alike, though -
> iridescent films have been reported on many freshly fallen meteorites,
> regardless of type.
>
> > 2a) This is where fusion crust might be found if there
> were normally crystalline molecules that melted and quickly
> quenched leaving an anamorphic solid. But what we know as
> true fusion crust is more complicated than that and is
> largely governed by the composition of the meteoroid.
>
> You breeze over it so nicely, without addressing the
> issue. Hum. Well, again, I don't know why you insist on the glassy
> nature of a fusion crust: I really can't fight your definition of it,
> because it simply doesn't make any sense. There's no reason to
> draw the line there, and I can't think of a single reason why fusion
> crust should *have to* contain glass. Knowing meteorites, I would
> define the fusion crust as the layer of meteoric material transformed
> into melt during a meteorite's ablative stages of flight, which later
> solidifies into a solid coating of material on the surface of the
> stone, iron, what have you. I see no reason to insist on glass - I
> agree that making a distinction between the properties of stones'
> versus irons' fusion crusts and their structures might well be a
> worthwhile endeavor, but insisting on calling the crust that forms on
> irons 'not a fusion crust' seems a pointless task.
>
> > 3)Flow/ Thermodynamic Features:
>
> > 3a)There may be a layer of flow streams/esker-like
> inverted stream channels where molten material, which
> escaped evaporation and,, was displaced from one spot to
> another where it may have been redeposited. Regardless it
> is an artifact of reentry and we may also include it in the
> subset of features we refer to as "flight markings" This is
> a gray area also because this is more akin to a surface
> feature than a true layer but I throw it out on the table
> for discussion. There will be occasional features which
> represent movement of material over top of a previously
> ablated surface and time and consensus will determine if it
> merits a layer designation.
>
> I disagree; such structures are merely features of the
> aforementioned fusion crust layer, and should be deemed synonymous with
> said layer.
> They are, after all, composed of the same materials, and
> one is not
> below or above the other layer; you're talking about the
> same stuff
> here.
> These features are made of the fusion crust noted above, so
> calling
> them a distinct layer seems pointless.
> You're not even arguing the difference between icing and
> frosting.
> You're arguing a difference between frosting and thick
> frosting. It
> just doesn't make sense.
>
> > 3b)There is also the occasional surface feature (semi
> flow) (which may or may not be a layer) of plastically
> deformed "ripple-marks" which give a satiny, wavy, micro
> "ridge and valley" pattern not unlike the depth and texture
> of fingerprints (NOTE this is not the same as "thumb-print"
> regmyglipts) Not all irons have this very thin layer. These
> ripple marks appear to form via fluid dynamics. I surmise
> (but have yet to prove) these are ripple marks of a
> extremely short-lived state where semi-molten metal is
> plastic enough to deform along lines where superheated gas
> eroding gas passing in both laminar and turbulent flow over
> the continuously evolving surface of the meteoroid. It
> leaves, a row and furrow/valley and ridge/ripple-like
> marking, submilimeter in depth. This results in that "less
> than glossy","satin-like" sheen seen on some
> meteorites--This is legitimate flight marking and therefore
> may actually be a surface feature and not a true layer but,
> a
> > variation on the ablation surface. I am leaning
> toward this being a surface feature vs an independent
> layer.
>
> See the specimen in my flickr stream pictured above.
> This "layer," as
> the one before it, is synonymous with fusion crust.
>
> > 4)Ablation surface: It is included to distinguish from
> the newly fallen surface any weathered/flaking/rusting
> surface all too frequently mistakenly called "fusion crust"
> on Canyon Diablos, Natans etc. Crust if present sits atop
> the ablation surface as it represents incorporated
> atmospheric gasses and possible re-deposition of Physically
> and chemically altered material from another location on the
> meteoroid, etc. Surface features can be in the ablation
> surface or above it depending on their origins. The ablation
> surface is a distinct demarkation between what was removed
> and what remained even if subsequently it bubbled into
> fusion crust or represents a redeposition of condensate from
> this ablative/ heating/ shearing process--which also needs a
> generic but descriptive name!
>
> False. Completely and utterly incorrect.
> You're talking about the surface of the iron meteorite
> itself, below
> the fusion crust.
> How on earth can you put this "layer" between the fusion
> crust and the
> reheated rim when many Canyon Diablos and Nantans have seen
> so much
> weathering so as to lose any trace of their original
> reheated rims!?
> The only irons I have *ever* seen to possess such a surface
> are desert
> irons, where the crust has been stripped from the fresh
> metal,
> allowing for a thin coating of desert varnish on the
> exposed iron (any
> substantial oxidation would destroy this "layer"), and on
> antarctic
> irons, where a similar process often occurs.
> Canyon Diablo and Nantan are examples of irons where the
> crust has
> been removed - along with countless mm or cm of
> material. This
> "layer," as you define it, does *not* exist on such irons.
>
> Oh - Sikhotes sometimes exhibit such a surface as
> weathering has
> removed patches of fusion crust while leaving the surface
> of the iron
> relatively unaltered. It's a good thing they're so
> fresh or this
> wouldn't be true...
>
> > 5)TAZ: Thermally Altered Zone: in this zone is the
> material which was not displaced nor reformed, per se-- but
> was thermally altered to a major or minor degree. Some
> volatile gases my have been out gassed but a major effect
> would be resetting magnetic orientation within the zone.
> There are means to analyze how deeply and to what range of
> elevated temperatures this zone was subjected to.
>
> Well, the major effect generally noted is the
> recrystallization of the
> meteoric material, but sure - this is a legitimate
> "layer."
>
> > 6) All the remaining material largely unaffected by
> the change in address from solar orbit to our collections. A
> place holder for the time being but all that which is not a
> part of the ablation zone.
> > I'll leave it there for tonight and for a straw man
> suggest there are 5 layers(on irons at least) in the
> "Ablation Zone". These layers are thick or thin; regions of
> original material which were in someway altered /affected by
> the dynamics of passage through the atmosphere.
>
> Right, well...you have my point of view. It's based
> on the fact that
> the fusion crusts on iron meteorites and on stony
> meteorites form
> through the same general processes into analogous
> structures and
> function in the same way on both types of meteorites.
> Your insisting
> on glass being a component of fusion crust seems as likely
> to be
> present due to a misinterpretation of some archaic article,
> as best I
> can tell, so I really don't know what to say. You
> keep stating the a
> fusion crust must contain glass 'because it is defined that
> way,' but
> when I stand back and ask the obvious question - 'why is it
> defined as
> such, and does that make sense,' all I get in response is
> a
> reiteration of your conviction that fusion crust is defined
> as such,
> and the definition cannot be changed.
>
> Science is change, Elton.
>
> The trouble with this point, though, is that you've taken
> up the
> conservative mantle of "no change" when I cannot find a
> single
> reference anywhere that states that fusion crust *must*
> contain glass.
> All of the literature from NIninger to Buchwald, to
> Krinov, to
> modern-day descriptions of meteorites entering the USNM
> from
> Antarctica - they all state that irons have fusion crusts.
>
> In other words, you're saying the definition shouldn't be
> changed from
> one in which glass is an indisputable component of fusion
> crust when
> that's not stated anywhere in the first place.
> You can't advocate *maintaining* a definition when it's
> *never* been
> accepted as fact, because that's not how definitions
> work. It needs
> to be accepted before you can try to "keep it
> accepted." Otherwise
> you're just advocating a new theory based on the historical
> merit of
> the theory - which, if it has never been accepted in the
> first place,
> is simply circular reasoning.
>
> You're the one advocating a backwards sort of change,
> Elton. We're
> going along with accepted meteoritics. And unless you
> have a reason
> to say that glass is an inherent component of what we are
> to deem
> fusion crust, I suggest that you come up with a better
> reason than
> "it's defined that way," because it's getting old.
>
> Regards,
> Jason
>
> > --- On Thu, 11/19/09, Martin Altmann <altmann at meteorite-martin.de>
> wrote:
> >
> >> From: Martin Altmann <altmann at meteorite-martin.de>
> >> Subject: Re: [meteorite-list] Fusion Crust on
> Irons--Not
> >> To: Meteorite-list at meteoritecentral.com
> >> Date: Thursday, November 19, 2009, 7:21 AM
> >> Unlike in politics and public opinion
> >> (and sometimes in science),
> >> in meteoritics it sometimes can be more difficult
> to adhere to
> >> theories/legends,if one gets samples in ones very
> hands, which exhibit the opposite of that, the theory
> postulates.
> >>
> >> If you ever had an early picked Sikhote at hand,
> >> or if you had taken from Andi Gren's Boguslavka
> slices
> >> (a fall, who simply hadn't enough time in field,
> to develop
> >> a magnetite, wuestite, limonite or whatever -ite
> weathering crust),
> >> you would be very surprised.
> >>
> >> Cause they don't display that ominous blue-ish
> flimsy
> >> luster, which is often reported as fusion crust,
> but a thick and fat layer of a discernibly different matter
> than the material beneath, of a dark color and rough to
> silky surface.
> >>
> >> I never believed in iron fusion crusts neither,
> but when I
> >> got in these freshly picked up observed falls, I
> was disabused.
> >>
> >> Main problem in that question is, as it was
> correctly
> >> mentioned here, that we simply have so few
> pristine samples of fresh iron falls and that most irons we
> get in our collections arrive with weathered or artificially
> cleaned surfaces.
> >>
> >> Now you may argue about the word "crust" as a
> >> (pseudo-)scientific term...well for me scientific
> terms are best, when they keep most of their meaning they
> have in their common use in the language. And there crust -
> meant for me a layer on the outside of an object.
> >
> >> .....and we have the problem, that there exist
> these
> >> freshly fallen lumps with that strange crust.
> Shall we hide them in the deepest corner of our drawers,
> cause they don't fit in the axiom, that fusion crusts are
> fusion crusts only, when silicates are melting?
> >>
> >> Sometimes, if the results don't fit into a theory,
> one has
> >> to think about modifying the theory,
> >>
> >> Else there wouldn't be no meteorites in our sense
> at all,
> >> Nada, Niente, Nix, Nimic, cause we all would know
> that they are products of our Aristotelian atmosphere,
> solidfied accumulations of terrestrial vapours and probably
> created by lightning strokes,wouldn't we?
> >>
> >> Best!
> >> Martin
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Received on Fri 20 Nov 2009 11:45:20 AM PST