[meteorite-list] Tektite surface morphology

From: James Tobin <jimmypaul_at_meteoritecentral.com>
Date: Thu Apr 22 09:42:06 2004
Message-ID: <3A738E90.9488883C_at_earthlink.net>

Hi Joseph, David, Tracy and List,
Paul and I had the pleasure of owning casts of the Nininger "gooey insides"
tektites for a number of years. Thay have now been sold but Michael Blood's
shows identical characterisics. Clearly the outside is detailed to a large
degree the way it was when it landed. I would submit as an added example the
incoming side of an australite button compared to the back side which is
surrounded by the encircling flange material. The back side very often is
old and rough looking by contrast to the ringwave surface which is smooth
and shiny. As pointed out before the entire tektite has been in the ground
exposed to corrosives for the same time frame. Yet there is little evidence
of etching in many cases on the ring wave surface. This has been suggested
to be (as is other pitting on indochinites) the result if slight differences
in the chemistry of various areas, some etching much easier. This idea has
especially been applied to Muong Nong layered tektites where complete layers
will look as if they have been eaten away. As far as regular splashform
tektites goes I find the preferential etching idea to be insuffient
explaination for the degree of pitting and grooving sometimes seen. I would
tend to go with a model involving cooling of the outside with cracking as a
result of stress, then shrinkage as the inside cools which pulls the
material down deepening the cracks and leaving "u" shaped bottoms which are
often seen. This model does not work for all tektites but works for many of
the Indochinites which should be least etched since they are youngest and
are in fact often sculptured to the extreme. Some tektites seem to have "v"
shaped bottoms in their groove also so etching by chemical means may be
responsible for the surface of some other tektites however.
It has been also suggested that the pitting is the result of spallation
during the passage through the atmosphere. That the unequal heating causes
concoidal pieces to pop out. It would seem that this would only be possible
if the forms were truly hard rigid bodies, the taffy pulled and bent ones
would cast some doubt as to their hardness.
We recently did an intense study with lots of photos of a large unwashed
Ivory Coast tektite which makes us think that the hemispherical pits are
perhaps the bottoms of bubbles that where ablated or actually broken off.
The bubbles cooled with very thin exposed upper halves. Some of these are
still visible and transparent just below the surface on this Ivory Coast. In
fact they can be looked into and through under a microscope.
The pits of tektites often have shiny surfaces not severly chemically crased
and dulled. Exposed, internal bubbles in broken tektites have a firepolished
luster which I think could be concluded to be how the outside may have
appeared when they were first formed. Comparing this pristine luster with
the good luster of the outside now causes me to think that many have had
only slight chemical attack.

This is an area that has been debated since the first tektites were found, I
hate to resort to saying that it is a combination of processes, but it well
may be. We recently got to see some man made glass which had been buried for
a very long time and I must say it was remarkably etched and even pitted so
hey make your own guess.

Hope to see some of you soon in Tucson, can hardly wait now.
Jim Tobin
The Meteorite Exchange
jim_at_meteorite.com

David Weir wrote:

> Hello Joseph,
>
> In a Science article titled "Tektites That Were Partially Plastic after
> Completion of Surface Sculpturing", July 7, 1967, vol.157, No. 3784,
> written by Nininger and Huss, this very subject was examined in light of
> two indochinites that show this type of streching while still in the
> plastic state. They state that if the tektites had been etched by soil
> acids, the stretch areas would have been etched to a similar degree as
> the rest of the tektite, which as Joseph points out is not the case.
> They conclude that what was previously thought to be etching by ground
> acids was actually due to aerodynamic sculpting. The internal heating
> demonstrated by the plastic stretching is also further evidence that the
> tektites did not arrive as individuals, in which case the only heating
> would be on the exterior from friction. Rather, they believe they were
> thrown off by a large rapidly rotating body within the atmosphere.
>
> David
>
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Received on Sat 27 Jan 2001 10:14:24 PM PST