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INDOCHINITE FORMATION

PLASTICALLY DEFORMED TEKTITES 

 

Indochinites are fascinating when you get to know and understand them. I am just at the beginning of understanding these tektites. Indochinites are unique compared to other tektites in that many re-entered the Earth’s atmosphere in a molten, or at least semi-molten, state. I have updated this page to reflect my current views. Some good Indochinite images can be found in an article by  Erland Damgaard Jenson.

When the asteroid impacted obliquely, tektites were formed from the uppermost layers of rock. The first ejected, at the highest velocities and highest temperatures, were the Australites. The last ejected, at reduced velocities and slightly lower temperatures were the Indochinites. The reduced velocities left little time for cooling and solidification before gravity took over and re-entry occurred. 

Firstly, before starting it is important to understand the orientation of indochinites. I run through orientation on the ‘Very Quick Guide’ page, but will repeat it here. On indochinites, as with all other tektites the smooth side represents the posterior (back). The anterior (front) is typified by a pock-marked surface surrounded on the edges by smooth areas known as bald spots. The pock marking undoubtedly arose due to the thermal stresses (both heating and cooling) of re-entry, probably acting on the original skin with no spalling (hence no U-grooves are developed). The bald areas around the edges arise due to thermal stresses acting on a very thin surface layer of glass. Bald spots always indicate the anterior of the specimen. Another clue is found on teardrop specimens. The tail, which is thinner and solidifies faster than the main body, always points to the posterior. Very rarely, Indochinites may develop an Anda-type sculpture. This is best developed on the posterior of the specimen. It is also commonly developed, although poorer, on the anterior surface (but not on bald spots). This attests to the surface of the central part of the anterior surface being un-spalled and primary in origin (probably protected by a pocket of air).



ABOVE: A Chinese tektite in side view (posterior at top, anterior at bottom) – note how the tail points to the posterior; Anterior view – note the pock-marking surrounded by bald edges; Posterior view – note the smooth surface.

Splashforms can be perfect primary forms comprising teardrops, dumbbells and spheres. These forms had likely cooled sufficiently before atmospheric re-entry to avoid distortion. For a body of fixed size, one would expect these to have been ejected at higher velocities and represent slightly more distal tektites when compared to ‘flattened’ forms. Assemblages, however, would be expected to be mixed with larger tektites, that would have remained hotter for longer periods, due to their low surface area to volume ratio, being ‘flattened’ and smaller tektites keeping their primary shapes, as these cooled quicker.

ABOVE: These Indochinites have solidified sufficiently before re-entry to retain their original primary shape (maybe because they are smaller than average, or in a more distal location). Only a small area, corresponding to the leading edge(s), is lost due to thermal spalling during re-entry. This forms the bald spot. These tektites are figured in their stable re-entry position. 

It would be interesting to view collections of tektites from well recorded localities in Indochina. One could then gain a better understanding of whether small specimens had solidified and kept their shape whilst larger specimens were more molten and distorted by atmospheric re-entry. One could then follow the trail in towards the crater – the smaller the specimens are, that show distortion and flattening, the closer the locality would be to the source crater. Tektites, however, often change hands a few times before reaching collections and rarely is the find site well documented. It is amazing how many Indochinites have made it to the Philippines, and were unknowingly being sold by the owners as Philippinites. This must be a much bigger problem on land were tektites transportation by merchants is probably considerable. Often if you can accurately identify the country or general region the tektite has come from then you are doing well.

Splashforms may also be ‘flattened’ or ‘squashed’. This results in ‘flattened’ teardrops (including ‘onion’-forms), ‘flattened’ dumbbells, ovals and ‘flattened’ spheres known as discs (biconvex, biconcave ‘donuts’, concavo-convex, concave-flat, convex-flat). The ‘donut’ and ‘onion’ forms have fascinated me for a while. They are unique to the Indochinese region and this gives a clue to their formation. I believe that the flattening of these primary forms occurred when the tektite re-entered the denser layers of the atmosphere in a molten state. The tektites re-entered in a still molten state due to ejection at lower velocities, giving limited time to cool before they started their re-entry. Size is also a factor, with larger specimens retaining heat, and therefore a molten state, longer. Clearly tektites that re-enter in a molten state are very proximal to the impact site.

ABOVE: These indochinites were molten when they re-entered the atmosphere. The denser atmosphere distorted spheres into 'donuts' (shown cut in half) as the glass sagged and from teardrops to 'onions' and dumbbells into flat dumbbells (shown in cross-section). Try my experiments below with washing-up liquid and water to see how droplets are distorted when they hit denser layers. At the bottom the dashed areas are lost due to thermal spalling. This proves that in the latter stages of re-entry the outer shell of the tektite had cooled sufficiently to become brittle, distortion happened in the atmosphere and not on hitting the ground.

Many people, at first, think that the distortion of the tektite shape occurred when the tektite hit the ground. This cannot be the case. Around the anterior margins the tektites often exhibit ‘bald’ areas. The key here is that these bald areas are not random – they only occur on the regions that would have been exposed to heating during atmospheric re-entry. So we know that before the tektite had completed it’s re-entry, a thin outer shell had solidified sufficiently to become brittle and suffer from thermal shock and the loss of a thin shell on the anterior margin. If this shell loss was unrelated to atmospheric passage then it would be random all over the surface of the tektite.

ABOVE:  A massive 497g Indochinite from Vietnam

I envisage that as these tektites re-entered at high velocities (and perhaps some never truly exited the atmosphere) they were distorted. If a man jumps into a swimming pool from a great height the water might as well be concrete. To a molten tektite, the denser layers of the atmosphere would have been like this, and the tektite was literally flattened. I believe that flattening occurred in a similar way to why Australite rims are flat – due to deceleration body force (see Chapman, Larson and Anderson, 1962, page 9). I think that as the tektite hits denser layers in the atmosphere a ring vortex forms and this creates the toroidal or donut shape. A fun experiment is to drop droplets of a higher density liquid into a lower density liquid and see what happens. I used washing-up liquid/soap (which was green), drop by drop into water. When the spherical droplet enters the water a donut shape is formed. Another example is the classic smoke ring a smoker can blow out of his mouth.

ABOVE: Mini-moldavites! This is an experiment dripping washing-up liquid into water. The droplets are distorted into teardrops and donuts. Hard to catch in a photo, so try this yourself! 

NEXT see this You tube video of an ink drop ring Vortex (I couldn't embed the video, so here is the link) http://www.youtube.com/watch?v=OrQKhCd1kyY

ABOVE: A great You tube video of a smoke ring. I think donut shaped Indochinites formed in a similar way as they encountered ever denser atmosphere during re-entry.

Teardrops form into ‘onion’ tektites by being flattened in the same way that donuts are formed. The delicate tail, which solidified much quicker than the main mass of the specimen is bent up backwards and, due to its solid state, is not usually fully incorporated into the main body. Interestingly we see the same in Indochinites as we see in Moldavite teardrops. One thing is clear: ‘donut’ and ‘onion’ forms are only found in proximal areas. Where tektites re-entered solid no ‘donut’ forms are found: ‘Donuts’ are not primary shapes, but secondary re-entry modifications to the primary shape, which was a sphere.

ABOVE LEFT: A disc from Vietnam with bald spots around the edges on the anterior surface.  ABOVE RIGHT: An 'onion'-form with bald spots around the margins of the anterior surface.

ABOVE: An amazing 'onion' type indochinite from north Vietnam. Check out the second image of the anterior surface. This surface was exposed to re-entry heating, resulting in loss of the anterior margins - these flat areas are known as bald spots. The central area on the anterior surface is pitted with etching. It represents the original surface - why didn't this flake away during re-entry? Well I guess a trapped pocket of air protected this central concave area during re-entry. This classic anterior surface is found wherever molten tektites re-entered the atmosphere.

Both ‘flattened’ tektite forms (which re-entered molten) and those retaining their primary shape (which re-entered with a solid exterior) show the bald spots, briefly mentioned earlier. Bald spots are typically found on the anterior margins, i.e. the areas exposed to frictional re-entry heating. The bald areas are simply areas where the glass has spalled due to the temperature differential between the interior and exterior of the glass as the anterior margins were re-heated during re-entry. You can think of these specimens as a type of core, but they have only lost a small amount of the body when compared to philippinites and australites. Why is this? Well, the indochinites were still hot during re-entry so only a thin brittle exterior could be broken, a plastic molten interior cannot be broken. Philippinites and australites re-entered as fully solidified spheres, indochinites were still hot and semi-molten.

ABOVE: A bald spot (flat area where my thumb is) on an undistorted asymmetrical dumbbell.

   ABOVE: Fall orientation of tektites.

A common feature on Indochinites are Starburst Rays or Star Scars, these grooves open up or become wider towards the point of origin. Radial Rays also appear to be closely related but have a consistent groove width from the distal part to the point of origin. I’m uncertain whether these are original or etched features. I strongly suspect that radial rays are etched fractures, starburst rays or star scars are more debatable and may be (at least in part) original. Starburst rays or star scars may be where the solid and brittle outer skin has split and exposed the molten interior. Radial rays may be the same, but just remain as a fracture and not an actual skin split. I am fairly certain that these radial cracks formed due to thermal shock and pressures of atmospheric re-entry and not due to impact with the ground. These radiating cracks only occur on indochinites and principally on Indochinites that have been distorted. In experiments I carried out, this kind of crack only occurs on hollow glass spheres. This is basically what I envisage here. A brittle glass outer shell with a soft molten interior. Heat it or hit it and it will break like this. During atmospheric re-entry the tektite encountered both re-heating and intense deceleration pressures (same as hitting the glass).

 

ABOVE LEFT: Starburst Rays or Star Scars.            ABOVE RIGHT: Multiple radial rays. 

Finally we come to true broken tektites. These must show a break with convincing angular distortion of the body, exposing a molten/plastic interior. Perhaps the best examples are to be found in Nininger and Huss, 1967. They found only two very convincing specimens in 50,000 specimens from Dalat, South Vietnam. In other places, however, these forms may be marginally more common. These forms almost certainly resulted through collision and probably resulted from a ‘hard’ landing on the Earth. Nininger and Huss concluded that as the stretched plastic interior had little sculpture, but the hard exterior did have sculpture, that the sculpture had formed in flight, prior to breakage, therefore sculpture was not due to etching. I disagree with this conclusion. I believe that the lines of weakness that the etching preferentially attacks had formed prior to breakage, but the sculpture had not yet formed and came later due to etching.

Indochinites regularly have shells and nuclei. The nuclei are commonly small in contrast to the Philippinites. The Nuclei and shell split apparently occurred after the main atmospheric passage – in the latter stages of flight or on the ground. The splitting, very similar to ‘onion-skin’ weathering is caused by stresses relating to the temperature differential between the exterior and interior. This results in cracking. Coming back to the etching it is clear that on the shells the concave surface is smooth whilst the convex (original outer) surface is pitted. This is due to etching attacking surface weaknesses probably caused by atmospheric passage. The interior – nuclei and concave surface of the shell, did not suffer the same exposure and therefore these surfaces lack points of weakness for etching to attack.

I have not yet mentioned Muong Nong-type tektites. For some, such as Darryl Futrell, they represented the best evidence of a lunar origin, for others irrefutable proof of a terrestrial impact origin. Muong Nong-type tektites can occur in large masses of many kilos, whereas it is rare to find a true tektite over a kilo in size. They are typically layered, not as homogenous as true tektites and often contain bubble-rich layers. Whilst most researchers accept a terrestrial impact origin the jury is still out on their formation. As Darryl Futrell pointed out, there is a great similarity between volcanic glasses and Muong Nong-type tektites. I would be interested to follow this up with further reading and research.

   

ABOVE:   A 1.5kg Muong Nong-type tektite exhibiting a polygonal shape (cooling contraction cracks?) and 'layering'.

Muong Nong-type tektites occur exclusively in areas proximal to the impact, i.e. only the Indochinese area. There have been reports of Muong Nong-type tektites in the Philippines, however I believe these to be false. Perhaps due to material being brought from Indochina (many people of Chinese descent live in the Philippines) or perhaps due to misidentifying terrestrial volcanic obsidian which is common-place in the Philippines. I have seen well over 200 kilos of Philippinites and never seen anything I would consider a Muong Nong-type. This is as expected, as ‘layered’ tektites should not occur this far from the source.

For me, whilst intimately related to tektites, Muong Nong-type tektites are really bordering on impactites and in fact may prove to be true impactites. For the present I am favouring the idea that Muong Nong-type tektites or ‘layered’ tektites represent later phases of ejected material, ejected at lower velocities and lower temperatures. The lower temperatures may have been insufficient to totally melt and homogenize the material. Other people have favored puddles of Muong Nong-type glass occurring on the ground, either through rain of molten microtektites or through direct heating by the blast/impact. Certainly some interesting structures have been found in Muong Nong-type tektites and I am hoping to read up and think more about these in the future.

I hope that this page has served some kind of an introduction to Indochinites. Indochinites are an area I wish to study in the future to improve ideas. I think there is a lot still to learn from them. Unlike Australites were you might need a wind tunnel costing a few million dollars, I think a lot could be learnt by playing around with molten glass, cooling it, dropping it, throwing it at different viscosities. Some basic experiments might provide some interesting answers.

PLEASE VIEW MY PRESENTATION (19 FEB 2011) FOR UP-TO-DATE DATA/IMAGES

IMAGE under modification - I am attempting to come up with a decent classification of Indochinites.

ABOVE:   An attempt by the author to classify the different Indochinite morphologies.

 

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