I thought this article was going to be easy, but things took a bad turn when I realized there is a lot about dumbbells I don’t understand. Even really basic stuff, like why the double “b”? Totally unnecessary. (All the dictionaries I checked think that I am wrong, so “dumbbell” it is.)
By way of introduction, the dumbbells of which we speak are meteorite impact-related glasses in the geometric form of an hourglass. They come in an amazing diversity of flavors and sizes. Figure 1 provides a notion of the size range. The big one at the top is the largest ever reported at 411.7 grams from Guangdong, China. In the center is a sweet Atacamaite weighing in at 0.3 grams. At the bottom (red arrow), I have drawn a speck about 1 mm in length representing a fairly large microtektite dumbbell. They can be half that size. All are well-formed, highly symmetrical dumbbells.
As for flavors, Figure 2 provides a broad sampling of dumbbells in our collection (with weights in grams shown). Note the 1 cm scale cube at the lower left.
A range of Indochinites from China and Thailand are shown in group 1. To date, no challenger has unseated the 411 gm behemoth as the largest known splashform tektite dumbell in the world. (Guinness World Records wouldn’t adjudicate this claim as they had no standards for comparison. Fair enough.) At the lower size extreme for Indochinites, surface pitting largely obscures good geometric form, so tiny examples that may once have existed have corroded to skeletal bits with little remnant shape.
Group 2 in figure 2 includes Australite “dogbones”, which are unique amongst dumbbells in their thermal ablation features. The thermal spalling of the Australites indicates that stable flight for tektite dumbbells was side-on (also ratified by the splatting deformation in many Indochinites). (See Tektite Teaser March 2018)
Group 3 includes two moldavites; the 24.8 gm piece is from Slavce and the 5.4 gram wasp-waisted jewel is from Chlum, both Czech Republic. If teardrops are the result of dumbbells parting, most Moldavite dumbbells parted. Teardrops are far more abundant than dumbbells, which are quite rare.
A lonely Rizalite represents group 4. As with most Philippinites it is ornamented with deep U-shaped grooves. This specimen was recently recovered by gold miners at Barangay Talusan, Paracale. Dumbbells seem to be a much smaller proportion of the Philippinite population than with the coeval Indochinites where they are quite a common morphology
Another single occupies group 5, a dumbbell impactite from Wabar crater, Saudi Arabia. I don’t know of any others. (See Tektite Teaser for July 2013)
Group 6 shows sweet little Atacamaites from Chile (still in study), presumably an impactite. (See Tektite Teaser March 2015)
The specimens in group 7 are different: they are volcanic fire-fountain droplets, but I have included them for their testimony. We know the sort of environment that spawned these, and it required no exotic vacuum or dispensation from on high. Spray glass in the sky and you will get some (tiny) dumbbells.
Group 8 is spurious. It is a beautiful little Sikhote-Alin meteorite dumbell, probably a purely coincidental shape that serves to remind us that just because something is shaped like a dumbbell it could well be dumbbellic to assume that it is a dumbbell like all the rest. Not all dumbbells are dumbbells.
Off in the uncharted corners of ancient maps was sometimes a sea serpent with flowery text reading: “Here there be dragons…”. We have reached that place. For starters, due to surface tension a blob of liquid would like to be a sphere. But in a blistering fireball it is torn this way and that. Oscillating in extremity, big blobs are unstable and are torn apart. They, having lost their form and balance, can wobble into prolate spheroids, and accelerating even more, can spin like an Olympic discus to form discoid patties, or if even less balanced, propeller-like cylinders form, extending and finally parting into paired teardrops. Just before breakup it passes through a dumbbell stage. I have previously supposed (and preached, as above) that dumbbells were the result of deformation while spinning like a propeller. But I am not so sure.
The idea of a microtektite dumbbell half a millimeter long, the size of a grain of finely ground pepper, cart-wheeling through the sky with centrifugal forces inducing longitudinal fluidal flow of molten glass towards the extremities— it doesn’t work for me. It is certain that the effects of frictional resistance and heat exchange are scale dependent. A grain of dust will not behave the same as a half kilo blob of glass. Not in a windstorm, and not in a meteoritic impact fireball.
Stretch marks and flow banding in the larger pieces mostly show simple stretching along the long axis. The bulbous “gibbosities” at the hourglass ends show longitudinal inflationary terminal enlargements (I could’ve said they expand like balloons, but that seemed overly sanctimonious when “longitudinal inflationary terminal enlargements” would do just fine).
Figure 3: “Behemoth”, the largest known splashform tektite dumbell in the world weighs in at 411.7 grams, and hails from Guangdong Province, China! —And in the left corner, there is no challenger. This is THE big one! Pushing a half kilo and flawless. Note the longitudinal stretch lineations and simple balloon-like flow banding at the dumbbell ends.
It is interesting that smaller specimens show increasingly less organized, more chaotic flow banding. Conspicuous flow banding is present in less than 10% of the dumbbells in our collection
Figure 4 is a detail shot of the flow banding in the smaller “terminal gibbosity” of Behemoth. I get the sense of an orderly inflationary flow of glass from the central waist region into the gibbosities. (I think I like that word).
In an internet search regarding the dumbbell morphology in general, I mostly found references to nuclear fission models and biological cell division illustrations, all things involving a longitudinal stretch and parting without any requisite propeller-spin. It got me thinking of an oscillating spheroid of highly liquid glass. Imagine it in a zero gravity environment, like a blob of water floating in the International Space Station. Add the echoing shock waves of a highly energetic impact. Like a soap bubble in the wind, the glass orb deforms, stretching into prolate spheroids this way and that. With increasing total energy, the deformations would become more extreme, finally parting the dumbbell form when the long axis of stretch reaches its elastic limit and snaps into two teardrops.
I am fascinated that virtually all complete tektites in their primary undeformed state possess an axis about which the stone is circular in profile. It is not always the long axis. In a discus-like patty, it is the short axis. In a dumbbell, a look down the long axis reveals the mathematical axis of revolution that defines the shape. Surely this has genetic significance. Was this a primary axis of spin? If so, the resulting forms would fall in a range from discoids to cylinders depending on the ratio of centripetal acceleration to centrifugal forces. But if the cylindrical axis reflects a spin axis, the associated gyroscopic effects would resist propeller-like spin. Or the propeller-like spin would preclude axial spin. You can’t have both at once.
I think strongly oscillating glass blobs behaved a lot like Niels Bohr predicted with regards to nuclear fission in his liquid drop atomic model, a familiar breakfast table topic everywhere needing little further comment. If Bohr was right, we might well add dumbbells at the scale of an atomic nucleus to our size range. There is something very fundamental about the physics of dumbbell formation. By merit of having solidified while in various stages of scission, tektite and impactite dumbbells provide tangible snapshots of the process involved. I am pretty sure it did not require a propeller-like spin. I am also sure that I know less about dumbbells than I once thought I did!