[meteorite-list] Australite Tektites

[Paul Harris]

James Tobin wrote:
> 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.
http://www.meteorite-times.com/Back_Links/2003/September/Tektite_of_Month.htm
http://www.meteorite-times.com/Back_Links/2004/October/Tektite_of_Month.htm
http://www.meteorite-times.com/Back_Links/2005/February/Tektite_of_Month.htm
http://www.meteorite-times.com/Back_Links/2006/December/Tektite_of_Month.htm
http://www.meteorite-times.com/Back_Links/2007/May/Tektite_of_Month.htm
http://www.meteorite-times.com/Back_Links/2007/June/Tektite_of_Month.htm

>
>
> 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
>
>
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