[meteorite-list] Atmospheric ablation marks on Tektites?

[Michael Gilmer]

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  
> 
> 
> 
> 
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>
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> 




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