[meteorite-list] Atmospheric ablation marks on Tektites?

From: Michael Gilmer <michael_w_gilmer_at_meteoritecentral.com>
Date: Sat, 5 Apr 2008 08:07:05 -0700 (PDT)
Message-ID: <559971.1924.qm_at_web58414.mail.re3.yahoo.com>

Hi!

Ok, now I figuring out this tektite issue. I want
to thank everyone for their kind informative
responses.

First, I had no idea that tektites were so
controversial!

Well, I did have *some* idea, but I thought it was
generally accepted by the meteorite community that
tektites of all types were impact artifacts and were
not the product of atmospheric-entry or
extra-terrestrial processes. I knew that there were
alternate theories for the origins of tektites, but
I thought these theories were mostly fringe in nature
and not commonly accepted by the Met community at
large. It appears I have a lot more reading to do
on tektites.

"Ventifact" does indeed seem to be the best term
available to describe regmaglypt-like features on
LDG and other similar glasses. Features that suggest
orientation or flow-lines are also wind-driven
ventifacts I assume.

As others said though, this does not reasonably
explain
the appearance of "button" tektites of the
Australite variety. Although I must admit, the first
time I saw a button-type tektite, my first thought
was not atmospheric-ablation or sculpting. My first
thought was a splatter-type impact artifact. If you
have ever taken a spoonfull of viscous batter and
dropped it on the floor, the outer edges of the mass
will spread outward while the central area is uplifted
somewhat. I had erringly assumed that similar
physics were at work with the button-types. Perhaps
a massive detonation on impact liquified a combination
of meteorite and earthly-minerals which were blasted
upwards and then fell back to earth - forming into a
button when the material hit the ground again.

Again, I expose my ignorance here. And I am glad I
came to the list with this question. :)

So while we are on the subject and educating a newbie
here, let me ask a couple of tektite-related questions
for the record, so to speak.

1) tektite and impactite - interchangeable terms or
different animals?

2) desert glass, darwin glass - terrestrial or not?

3) When describing aesthetic features present on a
tektite/impactite that resemble atmospheric effects,
should one use the term "pseudo-regmaglypts" or
"ventifacts"? Or should one go ahead and use the
same terminology used to describe these features in
meteorites? (orientation, flowlines, etc)

4) have impactites/tektites ever been studied in-depth
in the lab to determine their exact source? It seems
to me a minor mystery to solve. We can compare
chemistries of specimens to determine a lunar or
martian origin, but we lack the science to determine
where a tektite formed? I'm surprised this is still
a "controversial" issue - modern science has peeled
back the layers of confusion on deeper mysteries
than this.

Thanks in advance for putting up with this newbies
inquiries!

MikeG
 




--- Impactika at aol.com wrote:

> Hello Mike and List,
>
> There is some confusion here.
> Libyan Desert Glass is an impact glass, not a
> tektite.
> It is 20-30 millions years old, has gone thru many
> changes in climate and
> conditions in their corner of the Sahara. But in the
> last few thousands of
> years, it has mostly been shaped/ablated/sculpted by
> zillions of sand storms.
> More like Ventrifacts really
> Does that help?
>
> Anne M. Black
> www.IMPACTIKA.com
> IMPACTIKA at aol.com
> Vice-President of IMCA
> www.IMCA.cc
>
------------------------------------------------------------------------
>
> In a message dated 4/4/2008 8:37:13 PM Mountain
> Daylight Time,
> michael_w_gilmer at yahoo.com writes:
> Hi Group!
>
> While reading through another Meteorite-related
> message board on the WWW, I ran across a statement
> by
> an IMCA member that puzzles me somewhat. A
> discussion
> about Libyan Desert Glass was ongoing, and we were
> sharing photos of our LDG specimens. (and I showed
> off my new 9+ gram piece of dark-veined glass from
> Michael Farmer - thanks Mike!)
>
> So the guy says :
>
> "This is one of my favorites and is fully oriented
> with regmaglypts (yes, tektite impactites can have
> atmospheric ablation patterns too)."
>
> Ok, here is my confusion - I was under the
> impression
> that tektites were formed on impact - on Earth.
> So,
> doesn't this mean they cannot have atmospheric
> ablation patterns? Assuming the tektite never
> passed
> through the atmosphere, I don't see how this is
> possible.
>
> I have seen tektites with features that resemble
> regmaglypts and orientation, but this is just
> chance
> occurence, right?
>
> Or do I need to be schooled here?
>
> Thanks in advance!
>
> MikeG
>
>
>
>
> **************Planning your summer road trip? Check
> out AOL Travel Guides.
>
>
(http://travel.aol.com/travel-guide/united-states?ncid=aoltrv00030000000016)
>




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Received on Sat 05 Apr 2008 11:07:05 AM PDT