[meteorite-list] Australite Tektites
From: Paul Harris <paul_at_meteoritecentral.com>
Date: Sat, 05 Apr 2008 16:16:09 -0700 Message-ID: <47F80839.5030003_at_meteorite.com> 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 > > > ______________________________________________ > http://www.meteoritecentral.com > Meteorite-list mailing list > Meteorite-list at meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > > Received on Sat 05 Apr 2008 07:16:09 PM PDT |
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