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

[Greg Stanley]

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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