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

From: Norm Lehrman <nlehrman_at_meteoritecentral.com>
Date: Fri Mar 3 19:09:44 2006
Message-ID: <20060304000941.82702.qmail_at_web81009.mail.mud.yahoo.com>

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
> in such a great quantity that the
> energy is also enough to propel tektites into the
> upper atmosphere and have
> them re-enter ablating like meteorites.
>
> These are a bunch of hand-waving concepts, but as we
> know, it seems the one
> factor that really distinguishes "tektites" is the
> low water content. LDG's
> have at least 5 times the typical water content of
> the cleaner tektites, and
> they contain inclusions including those of the
> impactor, and aerodynamic shapes
> are not really known I believe.
>
> In fact the water content of LDG's at the low end of
> 5 times the amount of
> the cleaner tektites actually goes practically as
> high as obsidian. They don't
> usually look very aerodynamic and they have
> meteorites inside them. They
> deserve some distinction, they are dirty glass. Now
> all of this about water
> content might be just an academic distinction,
> except for one exception. One of
> the greatest mysteries of tektites is derived from
> the mystery of exactly what
> physical laws were twisted to get that low water
> content and this more than
> anything else is the criterion as much as the
> mystery. Plus they are generally
> clean (OK, they have smalled fused cuartz. etc., but
> there there tends to be a
> bimodal distribution between clean tektites and
> impact glasses as far as
> inclusions = so far you have clean ones and dirty
> ones) Please don't bring up
> layered tektites I don't want the definition system
> to fail even more...
>
> But practically speaking, you would have to be right
> that there is a
> continuum, just like in the definition of a planet,
> etc., the world tends towards
> complexity just when you get it all figured
> out...and soon we will come to know of
> the impektite that bridges tektites, water and all,
> with LDGs and other
> impact glasses. Better yet how about just saying
> they are all impact glasses -
> which they are no matter who starts talking about
> flying - and that tektites just
> had a higher energy/diffusion/flux melt event which
> is witnessed in the
> record by water content...If cats could only talk
> they could tell us how long we
> have erred on visible light as they see into the
> near UV, don't they? What's
> the use of going at it with a cat over the
> definition of "visible light"?:)
>
> My 2 centavos...Doug
>
Received on Fri 03 Mar 2006 07:09:41 PM PST