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

From: Greg Stanley <stanleygregr_at_meteoritecentral.com>
Date: Fri, 20 Nov 2009 09:37:20 -0800
Message-ID: <SNT117-W471C3CEE01B18644CA0A5ED2A10_at_phx.gbl>

List:

I think this one looks cool.

http://curator.jsc.nasa.gov/antmet/amn/AMNAug04/MIL03369.htm

Greg S.

----------------------------------------
> From: almitt at kconline.com
> To: mstreman53 at yahoo.com; meteorite-list at meteoritecentral.com; meteoritekid at gmail.com
> Date: Fri, 20 Nov 2009 11:45:20 -0500
> Subject: Re: [meteorite-list] Ablation Zone 5 Layers...Not
>
> 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"
> To: "Meteorite-list" ; "Jason Utas"
>
> 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 wrote:
>
>> From: Jason Utas
>> Subject: Re: [meteorite-list] Ablation Zone 5 Layers...Not
>> To: "Meteorite-list"
>> 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
>> wrote:
>>>
>>>> From: Martin Altmann
>>>> 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 12:37:20 PM PST