With Christmas looming (at the time of writing) I have taken it upon myself to destroy some baubles. At first I was deceived by some high quality plastic ones that I mistook for glass. Since then I have been able to acquire hollow glass spheres of two sizes and solid glass spheres of two sizes. The solid glass spheres cost about the same as tektites - a shame to destroy them really.
So, hollow spheres first. The size I opted to use was around 75mm diameter and comparable to a tektite of around 500g (if it were solid).
The first one I heated up to a high (unrecorded) temperature. The sphere hovered over the gas flame for a long time, but nothing happened - I was expecting a catastrophic explosion. Instead, the gradual expansion, caused by heating, appeared to be accomodated by the sphere. Then I plunged the glass into room temperature water! This rapid temperature change did the job and my sphere was well and truely cracked:
Next, I used the same size hollow sphere, but this time only heated it briefly and gently. Again, it did not crack until I quenched it in room temperature water. The result was a lot more similar to what we see in Philippinites, with the production of a polygon.
Next I attacked a solid sphere, by heating it in exactly the same manner. The solid sphere was 55mm in diameter and weighed in at 300g. The results were quite different to the hollow sphere. As you recall, the hollow sphere did not crack easily on heating, only when it was rapidly quenched in water. The solid, sphere, however, cracked, then rapidly flaked in an explosive manner. See the snap-shots below. The flakes came off individually or more commonly a few at once - and always catastrophically/explosively.
ABOVE: A couple of australite cores - remarkably similar to my glass core!
One has to bear in mind that the glass I used is different to tektite glass and in manufacture cooled in a more controlled manner. The temperatures used are different and the tektite was not travelling at hypervelocities when I did the experiment. Despite the many differences, I think we can glean a little about the properties of glass and how it cracks and breaks as a result of thermal expansion stresses. The solid sphere cracked in a remarkably similar way to australite cores - perhaps suggesting australites were fully solidified on re-entry. Hollow spheres behaved very differently. When I think of Philippinites I am guessing the hollow sphere scenario is more applicable. I am not saying that Philippinites were hollow, but that a brittle solidified outer shell enclosing a slighlty plastic, more molten, interior. This results in a cross between the hollow and solid sphere scenarios to explain the cracks seen in Philippinites.
Considering this, it certainly makes sense. Philippinites would have travelled to the Philippines in roughly one third of the time it took for australites to reach Australia. At 10 km/sec it only takes three and a half minutes to travel the 200 kilometres to the Philippines. On top of that, the lack of particles in sub-space results in an insulating effect on the tektite. It is highly feasible that Philippinites, whilst relatively solid, where not totally solidified on the interior at the time of re-entry. This results in cracking and some shell loss, but not in the same manner as in australites.
Please remember - if you choose to repeat these experiments at home, and I suggest you don't, then you need very good eye protection (fully enclosed googles, as glass can get behind eye glasses) and shielding for the rest of your body - glass explodes. Exploding glass can blind you and cut you. Girlfriends/wifes, whose kitchen has been destroyed, can do similar. These experiments are dangerous!