[meteorite-list] bubbly tektites

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 09:54:02 2004
Message-ID: <3C64A493.733282C6_at_bhil.com>

Hi, Graham and List,

    I was just waiting for the pissing match to end... if it ever does.
Meanwhile...
    Bubbles in tektites are not rare. In fact, there is an entire class of
tektites that is referred to as "bubble shards." These are the fragments of
tektites that were essentially no more than giant glass bubbles 20 to 50 mm
across (or larger). There are also tektites that are no more than a skin over an
intact bubble (rarer).
    You can do a quick sort for tektites that might contain large voids or
bubbles by simply dumping a bulk lot of tektites in a tub of water. A tektite
with a large void will float. Alternatively, just heft each tektite and set
aside for later density measurement those than feel much lighter than a tektite
its size ought to.
    In the case of bubble shards, the interior walls of former voids are
perfectly smooth and highly reflective. Such bubble shards appear to have been
broken recently (in collection) rather than anciently.
    Analysis of intact bubble tektites shows a very low internal pressure, about
the same as you would find about 25 miles above the Earth's surface. Most
analyses of the very small amount of gas found in intact voids show argon as the
predominant component, although there is one report of the detection of helium.
    Whether the gas is a "trapped" component or was produced by outgassing from
the material of the tektite is not known. Since many tektites are still plastic
when they reach the surface of the Earth, the bubble tektites must have cooled
to the point of material rigidity before re-entering the atmosphere, or they
would have collapsed. Since the cooling time to this temperature is quite long
in comparison to the supposed sub-orbital flight times of tektites produced by
an earth impact, this class of tektites must have had more evolved orbits than a
simple sub-orbital ballistic.
    Just one more of the many not-quite-explained characteristics of these
enigmatic objects.

Sterling K. Webb
---------------------------------------------------
Graham Christensen wrote:

> Hello Astro list and meteorite list,
>
> I discovered a few months ago as I was examining my tektite collection that
> one of the regular $5.00 pieces that you get from rock shops (indochinite?)
> has a bubble in it. The bubble is about 1 mm indiameter. Is a bubble like
> this rare? The tektite is an odd looking thing with huge pits (big enough to
> stick your finger in) on one side, and a light frothy texture on the other
> side.
>
> I have heard of bubbles in tektites before in an article I read somewhere.
> It said that the bubbles contain rarified ordinary air. If I remember
> correctly, this is believed to have resulted from the tektites forming in a
> column of low pressure air trailing the impacting meteorite. But wouldn't
> the low pressure air trailing the meteorite be dragged down from the upper
> atmosphere which has a different composition? I came up with a crazy
> alternative theory (I come up with a lot of these, too much spare time) that
> may eliminate this problem:
>
> In grade four, my teacher gave a science demonstration. She placed a metal
> container onto a hot plate, this heated the container and the air inside.
> Then she but a lid on the container and removed it from the heat source. As
> the air cooled it contracted, resulting in a lower pressure, the container
> collapsed. So, if a tektite solidified, somewhere under 2000 degrees, with a
> bubble in it, the air in the bubble would be at about 2000 degrees. Once the
> tektite solidified the air would be trapped in a bubble whose volume could
> no longer change. The air would still be at about 1500 degrees and when it
> cooled it would contract resulting in a low pressure within the bubble. Am I
> on to something or am I just crazy?
Received on Fri 08 Feb 2002 11:24:52 PM PST