A New Sort of Australasian Tektite Teardrop

There is a class of Indochinite teardrops that are commonly termed “Hershey’s Kisses” out of morphological similarities to their namesake. Some of these exhibit most unusual twisted tails, and this was to be an article about “twisters”, but I learned something unexpected along the way.

There is power in numbers, and as I gathered a broad selection of our Hershey’s Kiss tektites, I saw a rather constant theme. These are not teardrops as usual: there is something else going on here!

The tektite teardrop party line has always been that teardrops form when blobs of molten glass get a bit off-centered and extend into dumbbells spinning like airplane propellers, neck down in the middle, and ultimately part. I do believe this to be correct most of the time. But Hershey’s kisses are different. They constitute a special kind of their own on the basis of four criteria that I recognize:

1)  They have a distinctly bulbous, squat, pear-shaped, or even a flattened “puddle” profile.
2) They have a very consistent tail curvature. (See above image).
3) Their frontal surface shows deep beaded pitting and thermal spallation scars.
4) Nearly all show a variably developed skin lineation, like stretched or twisted taffy.

We have many hundreds of teardrops in our inventory. These are different. We don’t have any teardrops (other than those with the Hershey’s Kiss morphology) that show twists near their tails. We don’t have any dumbbells that show a twisted waistline, which would be a necessary precursor stage to an origin by necking and parting of a dumbbell.

The Hershey’s Kiss teardrops give the appearance of having formed in a very fluid state. The story that best fits our observations is that these originated in a very high temperature regime of the parent impact event. I envision blobular spheroids of liquid glass subjected to high velocity propulsion in a white-hot environment. Velocities were sufficiently high that the frontal surfaces of the projectiles built a leading face cushion of highly compressed air that variably flattened the nose. Pressure-shadow vacuum vortices formed in the rear. The still highly liquid glass was drawn into the tail vortex (with a profile likely related to projectile velocity), giving rise to long mathematically perfect tail forms. I further imagine that the airflow bordering the pressure shadow was in the form of a vortex. In this view, the skin lineations may well be low amplitude wrinkles resulting from frictional drag and deformation of a thin surface layer, although thermal erosion may also play a role (more on this later).

Interestingly, about half of our specimens show relatively straight longitudinal lineations. The other half are “twisters”, about evenly divided between clockwise and counter-clockwise spirals.

Thermal Ablation

These Hershey’s Kiss teardrops share a nearly universal frontal surface character which only revealed itself to me after inspecting over 50 of our best examples. Typically, the flattened nose is mostly bald, with patches that are deeply pitted with hemispherical cupules and/or grooves.

Often the shoulders have deep longitudinal gutters which open out into the tail region as if they were channels where airflow escaped from the compressed frontal cushion, jetting like a blowtorch around the edges into the pressure shadow vacuum. I consider these gutters to be thermal erosion channels. The tailward end of these gutters often serve as points or regions of origin for the skin lineations. In some cases, branching “tributaries” in the spill-over region coalesce to form more pronounced lineations in the tail section.

But the surprise came on closer inspection of the bald areas. Flake detachment scars are clear. These stones are not “bald”, they are ablated! These teardrops are a previously unrecognized type of thermal ablation core, quite like Australite ablation cores.

Spallation is a consequence of thermal differential. In the case of Australites, they came in icy cold, but the friction of atmospheric entry rapidly heated the frontal surface to incandescent temperatures. Simple expansion exfoliated wafer-thin spalls, such that the frontal surface of a well-developed core is ultimately devoid of any primary external skin.

The proposition that Hershey’s Kisses are thermal ablation cores raises an interesting question: this is the other end of the strewn field from Australites, so what is the explanation here? The spallation indicates temperature differential, a contrast in expansion and contraction. A frontal cushion of highly compressed air would have helped to maintain elevated temperatures in the underlying region of the tektite, while airflow around the flanks and tail would result in cooling and relative contraction. The bulbous distentional deformation of the nose would further encourage thin skin flakes to pop loose.

These “Hershey’s Kisses” are something special. They are nearly primary teardrops. The true primary forms were oscillating sub-spherical blobs of highly fluid glass battered by compressed air and stretched out in pressure shadow vortices.

Our specimens are mostly from Guandong Province of China, with a smaller number sourced from the Khorat Plateau, Thailand.

About the Author

Norm Lehrman is a recently retired exploration geologist with over 45 years experience. His career involved fieldwork in over 35 countries on every continent except Antarctica. While stationed in Australia, Norm and his wife, Cookie, became interested in collecting Australites, which ultimately led to a generalized passion for tektites, impactites, meteorites and related materials. In 1999 they founded the Tektite Source business (www.TektiteSource.com) which has evolved into one of the world's premier providers of tektite and impactite specimens. Norm has retired to a ranch near Spokane, Washington, where they continue to serve tektite aficionados worldwide.
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