Take a large piece of rock moving very fast and slam it into the Earth and you can make a crater, release tremendous energy, and kill everything for miles around. But, you probably will not make tektites. These peculiar pieces of natural glass have from what we can find, only been made by four impacts of asteroids into the Earth. During that period the Earth has been hit many more times than that. Why only rarely are tektites formed? That debate continues.
What we do know more about is the tektites themselves. The vaporous and liquefied rock is thrown high into the atmosphere nearly to space, where it begins to cool into glass. As blobs of this still plastic glass fall they are shaped by their size and spin into aerodynamic forms. Common types found are spheres, patties, dumbbells, rods, dog-bone shapes and teardrops.
Formation of tektite shapes through spinning is not that much different then what happens in many earthbound pursuits. Flat patties of tektite glass are formed basically the way pizzas are thrown. The molten glass is spinning in just one axis and the material spreads out by centrifical force from the middle. Other shapes form by different rotations. Teardrops for instance appear to be rod shapes which spun so that knobs formed toward the ends and stretched the middle thinner and thinner until the knobs completed separated into two teardrops. Should the cooling progress to the point that the glass is no longer plastic enough to continue stretching such a form may end as a dog-bone shaped tektite. Spheres seem to be blobs with low rates of spin in a random fashion so that no material is really thrown out. The glass just remains as a rounded blob.
All of the common shapes of tektites can be found with curves. Dog-bones and rods that are “c” shaped. Or patties that are dish shaped are common. Teardrops may have curved tails. This may indicate that they were still somewhat plastic upon reaching the ground and that they finished cooling and slumping with curves after landing.
Some patty shaped tektites have tears in the glass like radiating lines. On occasion you can also see the contours of a collapsed bubble in these. These may be hollow forms that upon hitting the ground ruptured and slumped.
Tektites are fascinating collectibles. Each is unique. Formed in the tremendous heat of a comic impact they seem to defy the rules of glass making as we know them in industry. But, we have them and who can say with the knowledge we currently possess what is possible when tens of thousands of degrees of heat are present.