[meteorite-list] moldavite splashforms w/ artifacts. Inquiry?

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:13:11 2004
Message-ID: <3EACB831.EE78AEBC_at_bhil.com>

Hi, Paul,

    Of the notion that differential chemical etching is
responsible for the surface features of tektites, there is no
proof. There is, in fact, definite disproof. In a paper published
in 1967, Nininger and Huss reported on their examination of
50,000 tektite and their surface features. They found two (yes,
two!) that had buckled upon impact while their interior was still
molten, leaving the two halves connected by a glassy bridge of
stretched material. The surfaces of these tektites were
fantastically "etched" but the glassy interior material was
mirror-smooth. Since both types of surface had been equally
exposed to the soil for 800,000 years, it is clear that
differential chemical etching cannot explain tektite surface
features. An illustration of one of these tektites can be found
in list member Guy Heinen's book "Tektites" (on p. 53).
    I have a tektite which is crudely lenticular (shaped like a
double convex lens). It is completely smooth and glassy
("unetched") except for two circular patches of "etched" surface
centered on each face. The explanation? It was a sphere, still
mostly molten with only a thin outer crust, that landed hard
enough to "squirt" its semi-liquid innards outward to form a
crude lens shape. (If it were a "spun" form, it would be much
more regular.)
    Even more compelling is an australite half-button (as opposed
to half of an australite button). There are numerous button
halves, meaning they were broken in half sometime later in life.
They show a smooth glassy fracture surface. But a half-button is
one split open while ablating. In mine, you can clearly see the
spot where the re-entry gas broke into the interior at the
forward face and split into "channels" as it forced the button
apart and etched the fracture face.
    Yes, many tektite individuals show fluvial abrasion that has
destroyed the surface sculture totally, but where this abrasion
has been mostly by small particles (sand), many feautures of
surface shapes may persist in outline. For example, I have
examined (under the microscope) many bediasites with heavy stream
wear that still retain their characteristic "fluted" or
regmaglyphed surface contours.
    Frankly, I feel that the popularity of the "differential
chemical etching" theory is due to its ability to dismiss in a
single phrase a complex morphology that defies easy explanation
and which has been inadequately studied. While aerodynamic
ablation is "probably" the answer, no one has undertaken the
monumental job of classifying and thoroughly explaining the great
variety of features that are to be found.
    Both the frequency of symmetry and the common orientation of
features on Besednice "leaf" moldavites argue against "corrosion"
as the sculpting force. Moreover, they are found in complete
range of forms from completely undamaged with every little
"finger" intact to progressively less and less elaborate forms
whose reduction is mechanical (breakage), not chemical. If
chemical etching were the formative agent, there would be
intermediately "etched" forms, and there are not. There would be
pieces only partially "etched", and there are not. There is no
evidence of a range of chemical activity, only of a range of
mechanical damage.
    Enough of another (friendly) tektite squabble.


Sterling K. Webb
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Paul Heinrich wrote:

> The impression that have I of the numerous specimens
> of moldavites that I have seen is that the vast
> majority of them are either deeply / severely
> etched or rounded by fluvial tumbling that nothing
> remains of their original surface morphology. As
> a result, so little remains of the original surface
> that it is very difficult, if not impossible, to
> know whether any molding of the typical moldavite's
> surface occurred upon landing. For example, the
> famous Besednice moldavites are **not** created by
> aerodynamic processes, but rather represent extreme
> chemical weathering (corrosion) of glassy moldavites.
>
> Yours,
>
> Paul
> Baton Rouge, LA
>
Received on Mon 28 Apr 2003 01:12:18 AM PDT