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This month we have the pleasure of getting to read and enjoy another excellent Tektite article from Jan Frank. Jan replied to my open call for articles and photos discussing possible theories for the type to tektite described below. One of the most rewarding aspects of collecting and studying Tektites is that all the answers are not know and one is free to explore the possibilities. The purpose here is to have the opportunity to hear different viewpoints and see other wonderful specimens so we may all expand our knowledge. |
I have a few samples which resemble those described by Paul Harris in his outstanding Tektite of the Month article from March 2003. I would like to introduce another theory which I believe fits better the samples from my collection.
On condition that a bubble of superheated, stressed, gas is just under the fresh solid surface and above the hot plastic core of the body, the whole system ie. solid surface, the bubble, and hot core is in equilibrium stage.
In this case, the solid crust cracks, the equilibrium collapses. Subsequently the plastic mass from the core of the tektite is pressed out to free space where it rapidly cools. This phenomenon is preserved on the surface of some tektites in different phases, depending on temperature, ie. plasticity of the tektite core.
But in this case the pressure in the bubble was not sufficient, or the core of the body was cooled off too much, and the classic concave surface of the vanished bubble could be preserved. In case, that the pressure was sufficient, but the core of the tektite was going to solidify, only a small knoll is developed and residue of the stress gets frozen in the mass of the tektite fig 1a-d.
 figure 1a |
 figure 1b |
 figure 1c |
 figure 1d |
| Click thumbnail for larger view | |||
In ideal case, when the temperature and pressure was sufficient for preserving plasticity of the core mass, the big knob is to be developed fig 2 b-e.
 figure 2b |
 figure 2c |
 figure 2d |
 figure 2e |
| Click thumbnail for larger view | |||
I was driven to these conclusions by two facts:
1) Convex surface of the knoll or knob (as a concave bottom of bubble) seems to be weathering-resistant and its sculpture clearly differs from the remaining surface of the tektite. That could be caused by different thermal history of both surfaces.
2) Visible marks of brittle fracture can be observed on the surface surrounding the knob, as Paul Harris stressed in his last article from this April . He described it as a mark of collision of two bodies. But in that case the surface of at least one of the bodies has to be cool and solid enough to allow development of brittle fracture. I think, in such case the two bodies could not have been "welded" together.
I suppose these are marks of peeling off the surface crust. However both of them are just theories and would need further research.
Very nice example of above described phenomena is exhibited at the Smithsonian Museum of Natural History in Washington, D.C. The pen drawing of it is on fig 3.
Figure 3. Pen
drawing
