[meteorite-list] Australite Tektites

From: James Tobin <jimmypaul_at_meteoritecentral.com>
Date: Sat, 5 Apr 2008 15:03:24 -0800
Message-ID: <00a201c89771$457f2c00$15998304_at_Jimscomputer>

Hi List,
Thank you Michael B for the kind words about my thin sections of buttons.
That was a long time ago. There is a micrograph of a picture of one of those
I still have in the September 2003 issue of Meteorite Times. If you go to
the current issue and use the link to back issues which is near the top of
the page under the rotation banner ads at the top center select article and
choose Tektite of the Month.

Here is a list of other articles with great pictures of buttons from Tektite
of the Month. Sorry I don't have time right now to copy all these links into
this message.

June 2007, May 2007, December 2006, February 2005, October 2004, and the one
mentioned above with the thin section picture September 2003.

The button type tektites would appear to be cold solid bodies that return
from near space at velocities high enough to ablate and the forward surface
melts. The liquid glass rolls up like a jelly roll often not welding well or
at all to the shrinking core body of the tektite. Often the stresses are so
great that the whole front of the tektite called appropriately enough the
"aerodynamic stress shield" will detach. The reasons for this are debated
still. I personally lean somewhat to a thermal shock of somekind between the
cold core and the heated outside. But would not get into a fight over this,
there may be a better reason for this detachment of the forward ringwave
surface and flange. The fact that many are found with adhering pieces of
ringwave and flange would seem to support that internal fracturing happens.
The flat surfaces characteristically seen on cores of ablated tektites
would indicate to me that fracturing happens as well.

If ablation continues long enough the rolled back material and the unwelded
narrow valley which forms next to the cold core will proceed to such a
degree that the bottom of the valley will actually reach the front surface
that is ablating and the ring itself can detach. Very rarely these rings
have been found unbroken as separate specimens. I have personally only held
one complete detached ring. But holding that one was exciting.

The ringwaves are a property that they receive from a combination of their
spin the motion of the liquid material that is rolling up and the air
currents against the face as it slows down and cools. Sometime this
intricate pattern will be very waffley if the flange itself is thin enough.
The ring waves are one of my favorite aspects of ablated tektites.

I will return to lurking.
Best regards, Jim
Received on Sat 05 Apr 2008 07:03:24 PM PDT