Tektite, anda, australite, philippinite, rizalite, bikolite, bicolite, indochinite, strewnfield, formation, sculpture, australasian, sale, bristol, impact, asteroid, meteor, meteorite, orientation, navals, grooves, bald, stretch, tektites, aubrey, whymark
INDOCHINITE FORMATION:
SPLATFORM & SPLASHFORM
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 and an alternate formation mechanism 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.
ABOVE: Typical Indochinese tektite morphologies derived from original splashform morphologies. I used to think, as this image suggests, that much of the shape deformation occurred on impact with the ground. I now believe that most occurred as the tektite re-entered denser atmospheric layers in a molten state. Please click on image for a larger version.
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.
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.
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.
Secondly splashforms may 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’ form has fascinated me for a while. I first considered that maybe it was due to the obliquity of the impact, with tektites shot off to the sides developing a rotation. Those shot forward would be spheres, thus explaining why we don’t see donuts anywhere else, other than in Indochina. This idea, however, was very unsatisfactory to me. I used to also think that the flattening of tektites occurred when they hit the ground, however, my ideas have now changed. 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 being molten due to ejection at lower velocities, giving limited time to cool before they started their re-entry, and also size being a factor, with larger specimens retaining heat longer. Clearly tektites that re-enter in a molten state are very proximal to the impact site.
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 wonder if the 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). Interestingly if this is an important factor one might consider that tektites ejected at a lower velocity might be less flattened.
I can see teardrops being flattened, with the delicate tail, which solidified much quicker than the main mass of the specimen, being bent up backwards. Interestingly we see the same in Indochinites as we see in Moldavite teardrops. Then we return to the curious ‘donuts’. For these I think of a chef making a pizza base, rotating the dough. The final morphology probably represents a complex of entry velocity versus rotational velocity versus cooling rate. As the ‘squashing’ combined with the rotational, centrifugal forces create a donut shape the thinner centre will now be acted upon differently to the edges, perhaps distorting a perfect donut into a concavo-convex form. One thing is clear, however, ‘donut’ 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.
So, why do I think that the distortion of the shapes took place during atmospheric re-entry and not due to hitting the ground? Well, superimposed on top of the distorted shapes we have bald spots. These are formed by ‘flaking’ of thin layers of glass. ‘Flaking’ takes place due to rapid changes in temperature. If tektites entered molten then the rapid change in by atmospheric heating would not have done a lot as the tektite was not solid and therefore not brittle. As the tektite was decelerated by the atmosphere it was probably cooling and by the time it had lost the inherited cosmic velocity it had, it probably cooled very rapidly. This difference in temperature between the interior and exterior resulted in ‘flaking’. As with other tektites, this ‘flaking’, although much more superficial, occurs primarily around the edges of the Indochinite.
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.
Tektites that appear to be less flattened and have more of a primary shape often have one end that is a bald spot. I used to consider this as due to distortion when the tektite impacted the ground. Now, however, whilst I still consider it a possibility, I consider these bald spots to have also formed by ‘flaking’. The forms that retained the primary shape better were probably much more solidified during re-entry, but nonetheless they may have been hot enough and therefore not brittle enough, not to undergo spalling like Philippinites and Australites. When the tektite had lost its inherited cosmic velocity it would fall dependent on centre of gravity. On a dumbbell the biggest end would fall be the anterior and would suffer the most thermal shock. Flattened specimens would have a different centre of gravity – this would be an interesting side study!
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. Radial Rays also appear to be closely related. I’m uncertain whether these are original or etched features. They appear to be original features where the solid and brittle outer skin has split and exposed the molten interior. If this isn’t the case then they are etched cracks, but essentially the same. It would appear that these formed on impact with the ground as the cracks radiate from a central point. Some tektites, however may have multiple starburst rays. Perhaps the origin is in fact again related to thermal stresses during atmospheric passage. Rapid quenching of a thin brittle exterior, whilst the interior is still molten, might result in this type of cracking. This type of feature is not found in other tektites, perhaps indicating that they had solid interiors during re-entry.
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 100 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 favoring 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.
ABOVE: An attempt by the author to classify the different Indochinite morphologies. Not updated recently and likely to be modified in the future. Please click on the image to see a larger version (opens new window).