[meteorite-list] Largest Crater in the Sahara Desert and LDG

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Fri Mar 3 22:16:38 2006
Message-ID: <BAY104-F25A7F261AAB27ECE613A89F8EB0_at_phx.gbl>

Maybe they're just kryptonite! Occam's razor. Think about it. ;]

http://theages.superman.ws/Encyclopaedia/kryptonite.php


While I only have one small sample in my collection, reading the bantering
about tektites on this List is always an interesting education for a rookie!

Cheers,
Pete




From: Norm Lehrman <nlehrman_at_nvbell.net>
To: MexicoDoug_at_aol.com,
bernd.pauli_at_paulinet.de,Meteorite-list@meteoritecentral.com
Subject: Re: [meteorite-list] Largest Crater in the Sahara Desert and LDG
Date: Fri, 3 Mar 2006 18:23:29 -0800 (PST)

Doug,

I do enjoy your contributions. Always stimulating.

I have no fundamental disagreements. Just a few
hair-splitting points.

Re: the partial pressures in Australasian bubbles. It
has been argued that our numbers are bogus. As
atmospheric water is absorbed into the hydrating
tektite selvage lining a bubble, internal pressures
can be considerably reduced, giving the false
appearance of high altitudes. I have never seen
anything about partial pressures in LDG glass. I'm
not sure anything has ever been found sufficiently
large to measure. Lacking such data, this argument
is conceptual, not real. However it is a great
research suggestion. With modern micro-techniques LDG
bubbles should be revisited!

As for a "real strewnfield defined for LDGs as we find
with other conceptually true to form tektites", yes,
the finding area is quite sharply delimited at about
150 km X 50 km. If anything, the LDG area is
atypically WELL defined relative to other tektites (I
don't know much about Ivory Coast distribution. It
may be comparable or smaller).

I must admit, I have never seen anything even remotely
resembling an erosionally-modified aerodynamically-
shaped Libyan Desert Glass form. If you started with
the typical morphologies of Australasians and
sand-blasted them within an inch of their existence,
we would still recognize some traces of original
morphology. I must decline any hope of the Harvey
Award on this matter. You are totally correct. LDG
shows absolutely no hint of aerodynamic ablation
modification.

Deep enough,
Norm
http://tektitesource.com (a great place to view a
huge selection of prime Libyan Desert Glass!)



--- MexicoDoug_at_aol.com wrote:

> Hola Norm, so it seems we actually agree on most of
> the points, including the
> most important one: the subjectivity of the
> definition. You are just wanting
> to be more liberal...and me more stoodgy...I wasn't
> dodging the layered
> tektite issue when I said not to bring it up (which
> you unfortunately did:)).
> Clearly layered tektites are closer to impact
> glasses in the continuum and I was
> just trying to cleanly conceptualize. The
> definition of 'tektite' is a human
> classification which like most, depends on a clear
> understanding of a concept,
> not a recipe. The Muong Nong glasses (vs. tektites)
> as many experts also call
> them deserve a category by themselves so if you want
> to point to experts
> calling them tektites as support for calling the
> LDG's also tektites, all I can
> say is we are pushing the concept even further. You
> do mention the meteoritic
> content of Indochinites (=Australasian tektites).
> Yes a small component of
> iron has been detected, but this is very rare, and
> no where near the content in
> LDG which can approach a 0.5%.
>
> You didn't mention that the partial pressure of the
> air in the bubbles of the
> Indochinites corresponds to the upper atmosphere,
> and that in LDG I am
> assuming it corresponds to the surface. This
> shouldn't be a surprise as the water
> should not be linearly independent - thus they ought
> to track similarly.
>
> Good point on the desert weathering, but is there a
> real strewn field defined
> for LDG's, as we find with other conceptually
> true-to-form tektites (pun:))?
> If any evidence could be found, your argument would
> be more solid, as a of
> evidence isn't any proof of anything. Try checking
> nobel gas ratios and I bet
> the tektite concept will be even further away...
>
> Where I must really agree with you and put all
> grammatical gymnastics and
> opinions aside, is where you make the best point of
> the whole discussion, imho.
> That maybe our definition of tektites whatever that
> concept may be is based on
> faulty ideas. With liberty taken, that maybe it
> will change as we learn
> more. Yes, I buy that, I believe that is a distinct
> possibility. Things were so
> much simpler when we all agreed they were blasted
> from the Moon and the
> aerodynamic shapes and low water content actually
> meant something more to the
> experts of that time. Gor the time being, I be
> conservative on the definitions for
> the distinctions mentioned. Show me one
> aerodynamically shaped LDG besides
> one sculpted by a Neanderthal, and I'll recommend
> you for a Harvey award which
> would be quite fitting:), and definitely a nobel
> prize in the meteoritical
> community...for the moment we think there is a
> crater now, well, we already called
> them impact glasses, and now we have all these years
> of human transport
> mucking it up for these highly prized special
> glasses.
>
> Perhaps little Norm and little Doug in the 100th
> century will follow in our
> footsteps. Norm will say, Doug, look at all the
> chondrites in the USA, and
> there are none in the Sahara. Looks like the major
> strewn field is into North
> America and then a minor one into Europe. And Doug
> will say, I don't know, they
> weren't witnessed falls.... Jokes aside, the
> concepts are pretty clear ---
> high energy, less meteoritic content, water content
> too low for earth's surface
> under all available explanations, aerodynamic
> shapes, minimal nobel gas
> concentration typical of higher atmosphere, upper
> atmosphere
> pressures(=low)...where does LDG have a positive? A
> crater in the same environment///I'll sit this
> one out on the fence...but note it duly with
> curiosity and opportunity...
>
> Saludos, Doug
>
>
> Norm L. wrote:
>
> <<Doug,
>
> Good points all, but if you want to raise the
> water/purity issue, you can't dodge the Muong Nong
> issue. (The best answer is that they shouldn't be
> called tektites, BUT, they ARE so called by all
> authorities).
>
> With LDG, it can be reasonably argued that
> flight-related morphology has been erased by
> ventifaction. In the area where this stuff is
> found,
> it is literally reasonable that ALL of the material
> has seen the wind and its entrained sand. LDG is
> pretty fine, clean glass, albeit with a higher
> water
> content. (So, here again, people have dodged the
> issue
> by calling them Muong Nongs---)
>
> As for inclusion of impactor material in LDG,
> you've
> got to remember that iron spherules are found in
> Australasian tektites. Good chance that's impactor
> condensate.
>
> I truly have no argument with the water content
> criterion. That's probably the best definitional
> parameter we have. But it makes me a bit nervous
> to
> turn the whole matter over to such a narrow
> definition. Are we positive, given all that we
> don't
> know about tektites, that there can't be any wet
> ones?
> Should we now start calling Pyrex another variety
> of
> tektite? Clearly, we are including some
> process-related factors (even if just inferred) in
> our
> definition.
>
> It is very much like the planet issue. I keep
> thinking that there have been a lot of grade-school
> kids that got marked down on tests for answering
> the
> question: "How many planets are in our solar
> system?"
> wrong according to the erroneous wisdom of a given
> time. How many tektite-producing impacts have
> there
> been? I get weary of qualifying my answers with,
> "Well, depending on whether or not you count
> LDG----"
>
> Cheers,
> Norm
> http://tektitesource.com>>
>
>
> --- MexicoDoug_at_aol.com wrote:
>
> > Norm L. writes:
> >
> > << Where is the dividing line between impactite
> and
> > tektite? I'd like to hear what others may
> > understand,
> > but my impression is that it fundamentally
> hinges
> > on
> > distance the glassy material is ejected from the
> > crater. Material found only in and immediately
> > around
> > the source crater is impactite. Stuff blasted
> tens
> > to
> > hundreds of km or more crosses the definitional
> > boundary into "tektites".
> >
> > If this is the criterion, LDG was already home
> free
> > >>
> >
> > Hola Norm, yet again here's another one of those
> > awkward definitions that
> > when overyly analyzed starts falling apart. I
> think
> > the distance criterion is
> > not THE criterion, but rather a tektite differs
> from
> > an impact glass in that the
> > tektite has actually been exposed to general
> > conditions of enough kinetic and
> > thermal energy to create a greater melt
> uniformity
> > where the original
> > impactor has transmitted that energy "cleanly",
> and
>
=== message truncated ===

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Received on Fri 03 Mar 2006 10:16:29 PM PST


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