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

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Fri, 20 Nov 2009 10:25:20 -0800
Message-ID: <93aaac890911201025s2d4c425fxc8d9f1daf9fdb1a6_at_mail.gmail.com>

Al,
Perhaps you should have read my last message a little more thoroughly as well.
I went out of my way to clarify. I even said the following:

"Not a single person on this list is saying
that all iron meteorites have fusion crusts, just as not a single
person on this list has ever said that all stony meteorites have
fusion crusts.
My point of view is that generally speaking, when an iron meteorite
falls, it is covered by what is deemed a fusion crust (barring
extenuating circumstances like an explosive impact [eg. Sikhote
shrapnel], or extremely late atmospheric fragmentation). Just as most
stony meteorite exhibit a fusion crust as well (barring an explosive
impact [eg. Carancas], etc, etc)."

I further stated that:

"Well yeah. Rust isn't fusion crust, but I might as well ask you if
you think that taking an acetylene torch to a stony meteorite and
melting its surface would create a fusion crust. The key, I think you
would agree, is in its method of formation...."

So, no, I don't believe that all iron meteorites are covered by fusion
crust. Just the fresh ones, assuming they're not the product of an
explosive impact, late fragmentation, etc.

Do you disagree?

Jason


What Elton is suggesting is that

On Fri, Nov 20, 2009 at 8:59 AM, al mitt <almitt at kconline.com> wrote:
> 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
>
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Received on Fri 20 Nov 2009 01:25:20 PM PST