[meteorite-list] Atmospheric ablation marks on Tektites?

From: Sean T. Murray <stm_at_meteoritecentral.com>
Date: Fri, 4 Apr 2008 23:13:20 -0400
Message-ID: <004a01c896cb$00a91e70$6501a8c0_at_platinum>

Ok folks - I want plenty of comments on this mess :) One of my favorite
topics... Let's see if I can ramble through this...

Most tektites, by definition, have passed through the atmosphere at least
once. Some material (depending on the theory you believe in) just is spit
out in the form of blobs of glass, but others take the long trip through the
atmosphere to gain their unique shapes.

There are still people on both sides of the fence as to the origin of
tektites. The majority of the folks think they happen on impact here on
earth and that the material is thrown out of the atmosphere and then
re-enters to create many of the aerodynamic shapes we see in typical
tektites. The other theory is that tektites were formed from lunar events
(such as volcanic eruptions) and enter the atmosphere on earth and gain much
of their shapes on the trip through.

There is a lot of reading material out there that talk about both theories.
The main flaw in the impact theory has to do with Stokes Law (for creating
glass) and the lack of a discovered crater for the Australasian event (the
crater should be massive considering tektites from that event covered about
20% of the planet). The lunar theory has it's share of problems as well.
You should read Hal Povenmire's book. It's got a lot of interesting
information on tektites. I also love this website:
http://www.tektites.co.uk/index.html - there is a good set of pages that
describe the formation of the shapes and features on tektites
(http://www.tektites.co.uk/22.html).

However, in the case of LDG, a point to make is that I've seen multiple
people argue that they are not actually tektites, but are instead impact
glass. Most impact glass definitions that I have seen don't require that
the material has been in and out of the atmosphere at least once. However,
it is hard to argue with the features on the LDGs. I have a piece that has
"regmaglypts" that rival any Sikote you can find (thanks to Mike as well!
http://www.rocksfromspace.org/March_23_2008.html). I called them "Pseudo" in
the description, because, well, there is still a lot of debate about them
being formed from traveling through the atmosphere, or just weathering out
due to natural weaknesses imposed by the cooling, impact, and subsequent
chemical etching (fresh water mainly) and/or sandblasting over the years.

I'd love to hear some other opinions. There is another source that I have
not started reading yet - Joe McCall's book on tektites. He does have a
chapter that singles out Darwin glass and LDG.

Sean.

----- Original Message -----
From: "Michael Gilmer" <michael_w_gilmer at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Friday, April 04, 2008 10:36 PM
Subject: [meteorite-list] Atmospheric ablation marks on Tektites?


> 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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Received on Fri 04 Apr 2008 11:13:20 PM PDT