[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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