Flanged Australite buttons are perhaps the most coveted tektite morphology that exists, and they are, indeed, glorious things. But they have an occasional offspring that is much, much rarer: the detached flange ring.
The majority of Australites appear to have started atmospheric re-entry as spheres, which were always thermally modified in subsequent gravitationally-accelerated flight. Flanges formed (and were sometimes preserved) in Australites of a very narrow initial size range. Above a certain size, temperatures were unable to equilibrate between the red hot frontal face and the vacuum-refrigerated posterior of the tektite. This thermal stress led to the explosive spalling of flakes from the expanding leading surface and the formation of fluted ablation cores. Within the critical dimension range, thermal stresses did equilibrate sufficiently to preclude breakage, and molten glass from the face flowed into the pressure shadows ringing the shoulder to form coiled flanges of secondary glass. But very often, the process went too far, and the flanges themselves were ablated away, leaving the most common Australite morphology of all, the discoid lens.
But what of the lost flanges? Once in a great while, they detached intact and survived as perfect rings. These are rare treasures and it took me over 20 years to acquire the specimen featured in this article. So far, I have never had another opportunity to obtain another one at any price.
All specimens are from the author’s private collection. The detached ring weighs 0.9 grams.