Spent a week making slices of Muong Nong Layered Tektite that were thin enough to see through easily. I do this every decade or so. It is hard work and time consuming. They can break easily if I am not careful since they are glass and only .020 -.030 inches thick. They are quite fragile. We know that they are not everyone’s cup of tea and the slices are not inexpensive. But if you love tektites it is cool to be able to see down inside the glass at how it is made.
Muong Nong Layered Tektite like Darwin Glass, Libyan Desert Glass and the many impact crater glasses presents an interesting problem for definition writers. While tektites would generally be required to have fallen through the atmosphere and received some shaping from their flight. Muong Nong Layered Tektite and some other glasses do not have real flights at all. Generally, these glasses are considered to have formed at or near the impact location. The crater glasses are in fact found around the craters they are associated with. But there is no currently known crater location for the huge strewnfield of the Australasian Splashform Tektites or the Muong Nong Layered Tektites of the same region.
The Astralasian strewnfield of tektites is enormous extending from far into China down to Australia and westward some think as far as Tibet and out toward the east into the western Pacific Ocean where tektites are found on many of the islands. Microtektites have been found in the Trans Antarctic Mountains extending the symmetry of the strewnfield southward further supporting an epicenter for the cosmic event in SE Asia. These are also the only microtektites to be found on land. (Falco et al 2008) Approximately one tenth of the surface of the Earth is within the area of this strewnfield. But the Muong Nong variety of Australasian tektite is not found over nearly as large an area.
Is this layered tektite glass the result of pooling and flowing of liquid rock melted at the location of the impact? That would seem to be the understanding accepted by most tektite researchers. Though there have been some other thoughts over the last hundred plus years that this glass has been studied. Some questions about this material continue to resist solution. The lack of a crater for such a huge event being perhaps the biggest unresolved problem. With an age of only 770,000 years give or take, these are among the youngest of the glasses and clearly result from maybe the largest tektite forming event, and no crater. Is the crater offshore? Has it been eroded completely away despite the short time frame? Was it as a few investigators think an airburst event?
The volume of Australasian tektite glass and area of distribution are so great most investigators do not think an airburst was the cause. As to the total mass of the material. Based on the microtektite abundance it has been placed at 2.7 x 10 E16 grams. (Schmidt and Wasson 2008)
Muong Nong Layered Tektite is as the name describes far less homogeneous then the splashform tektite glass. It is streaked with bands and swirls of glass from dark brown to nearly clear and all shades of yellowish-brown in between. It is far more bubbly than the splashform tektite glass. And where the splashform glass will show schlieren lines when examined in thin slices, Muong Nong type glass has different characteristics. It does not have the clarity that splashform tektite glass does. It is instead murky, cloudy and bubbly with some tiny dark bits enclosed within it.
It seems good to devote a few sentences to the chemistry of Australasian tektite glass. Muong Nong type glass has the highest SiO2 content. The range of SiO2 for Muong Nong across the strewnfield is 68.2 – 82.57% with an average being 76.6%. By contrast the SiO2 content of splashform glass across the strewnfield is a range of 62.2 – 79.7% with the average being 72.39%. The greatest variations in SiO2 content are found in the microtektites and that amount can be far lower than the SiO2 content of the other tektite glass types. The microtektites can also be enriched in MgO and FeO compared to the splashform and layered glass.
The chemistry of the glasses has been used to determine the source for most of the tektite strewnfields. Moldavites are associated with the Reis impact in Europe and the Ivory Coast tektites are the result of Bosumtwi Crater’s formation. North American tektites the Bediasites and Georgiaites are from the impact which formed Chesapeake Bay. In the case of the Australasian tektites the crater is missing so far. However, as with the others the chemistry of the glass is consistent with the target rocks of the area around Northeast Thailand, Laos, Cambodia, Vietnam and offshore Vietnam. Some investigators have noted subgroups of composition which have presented some problems for explanation. For example, a High Mg group, a High Ca australite group, and a High Ca philippinite group have been suggested.(Chapman and Schreiber 1969) What is more clear is that the composition of these subgroups overlap across the strewnfield. The most reasonable explanation to this writer is that there was little mixing within the impact plume. The composition of the glass has with broad strokes recorded the chemical differences of the target rocks across the very large impact region.
I have written along with others about the problems of cutting splashform tektites which have not been annealed in a furnace. As the inside and outside of the blobs of splashform glass cooled and became rigid at an altitude maybe near or in space, the areas cooled differently. This created strain within the glass. The individual splashform tektites are able to handle this strain safely since the thick outer glass is very strong. But when the piece is cut and that outer layer is ruptured the twisting and pressure of the strain can shatter the specimen. I have had pieces explode in the saw. This is always shocking the instant that it happens. I have had many slices of splashform tektite actually survive cutting, lapping and polishing to around .020 inch thickness only to have them crack while sitting untouched on my desk a day or two later. Even in thin slice that strain is there. However, Muong Nong Layered Tektite presents no stain related problems to me for cutting. It has other issues that make cutting difficult.
Often Muong Nong Layered Tektite is heavily etched and therefore very weak in many areas of a single specimen. Often chunks are impregnated with lateritic soils that have hardened to stone. This laterite is filling voids and cracks. This makes many flaws invisible before cutting. Many times the specimen will be partially held together just by the red lateritic soil inclusions. Some pieces on the other hand are round lumps with no soil and little etching and cut easily. These are sometimes not the ones that show the characteristics that make this material so interesting under a microscope. These unetched laterite free specimens often do show the greatest range of colors in their banding and often have the lowest amount of bubbles. So in their own way these are also very interesting under a microscope.
While we usually think of Muong Nong type tektite as being from the Australasian strewfield, layered type glass has been found as a small sampling from some of the other tektite strewnfields as well. There have been recovered a few pieces of Moldavite that have a layered appearance also some Bediasites that look layered. Libyan Desert Glass sliced thin will show a similar layered appearance to Muong Nong glass under microscopic examination. However, with LDG there is not a lot of variation in color from layer to layer. I personally have little difficulty considering LDG to be material from a melt sheet that flowed and puddled similarly to what is thought to have happened with the Australasian Muong Nong type glass. In the case of LDG the air burst explanation for the event may be the best choice from what is known at this time.
Muong Nong Layered Tektite glass is low in water and as discussed already chemically similar to the splashform glass. It is very different in color and nature from terrestrial glasses mainly represented by all the obsidians. Decades ago a volcanic origin was considered for tektite glass and proponents often used Muong Nong glass for many of the ideas the theory purposed. The Earth was not the source of the glass however. Instead the volcanic activity of the Moon was thought to have formed the Muong Nong type glass. It was thought to have arrived on Earth as impacts of large masses of Lunar volcanic rocks. Ideas like welded microtektites being the tiny structures from which the large masses were formed were held by some individuals. Even though I knew one such individual very well and spoke to him at length I never saw in the microscope what he was calling a microtektite. The layers in Muong Nong type glass always look like a continuous band of melted glass with other layers above and below. The overall mass punctured with numerous holes and bubbles and etched away in a manner that appeared to me to be the result of layers having differing resistance to attack from chemicals in the soil.
Tektites and crater glasses remain an exciting area of interest for collectors. They are not meteorites and may or may not contain material from the asteroid that liquified and vaporized in the impact. But it is clear that they did form in an impact event. It is also clear that these events were off the scale we normally think about for temperature and energy. But even as high as the temperatures are the volatilization and elemental depletion for all elements less volatile than Phosphorous is still minimal. This makes connecting the glasses to target rocks a reliable method for determining the source crater. It was this type of analysis along with the returned samples of lunar rocks that placed the origin of tektites solidly on the Earth.
There are plenty of things to contemplate while looking at these strange objects. How did they get their shapes? Were they just liquid or vaporous before they cooled? How high toward space did the material go up? Did they all ablate some during their fall to the ground? Or did only the Australites ablate. What was special about the material that headed toward Australia that it formed flanged tektites? Are other zones of ablated tektites out in the ocean? Why are there only a few places from a handful of impacts that have tektites while there are vastly more impact craters? Why is Muong Nong type glass almost only found at the one event of the indochinite tektites? And was the Muong Nong material once a continuous sheet that has broken up or was it always somewhat discontinuous? A person can spend years reading works written about research into these questions.
August is the time some of us remember Darryl Futrell’s passing. He was a lifelong collector of tektites and related rocks. He held views that became less than popular as the years went by. Our visits to the Moon and the samples returned from there did bring an end to most of the debate about the origin of tektites. That is not to say that all the answers were discovered about them. But their origin as being from melted terrestrial material was quite settled. For most individuals except Darryl and a handful of others the Moon was no longer a candidate for tektite origin. Darryl never did give up his belief in a lunar origin. I remember him telling me what he thought happened on the Moon. He envisioned a volcanic vent that spit out streams of glass as microtektites that fell onto a growing molten mass. This went on for eons forming huge amounts of rock. I asked him right out one day if he thought that impacts or later volcanic explosions had blasted this material off the Moon. He said “yes giant blocks of this rhyolithic like rock was sent out into space and then hit the Earth.” As I said before I have never seen what he saw in the glass. Yet he did know more about these bits of glass than most people. He clearly had more of them to look at then nearly anyone else. He wanted answers to a few remaining questions that he had. He thought these questions were still best solved by an origin off our world. I guess I admired Darryl for his honest pursuit of knowledge in a climate that was getting more hostile toward him all the time. I remember reading some rather sarcastic remarks in scientific journals about a problem tektite that did not fit the new models. How it was hoped by the writers that this tektite would not revive an old dead theory like Lazarus rising from his grave. It always seems to me unprofessional to try and squelch debate with sarcasm and ridicule. Darryl never involved himself in that sort of thing. He took I think little note of the comments. He just seems to have loved the tektite mystery and sought to discover whatever he could about them. It has been years since Darryl passed away but Paul and I are still surrounded by a remaining portion of the tektites that Darryl had amassed. It is hard not to think of him every time I load a piece of Muong Nong into the saw or clean a batch of splashforms for sale. I emptied onto a table one of his ancient wooden crates that had been used to ship his tektites from Thailand. It held large pieces of Muong Nong. I was looking for pieces to cut and polish. But once again I was presented with specimens just too big and too nice to cut. I guess I got some of that respect for the stuff that Darryl had and it is hard to slice some of them up. Tektites are not everyone’s cup of tea and giant pieces of the Muong Nong type maybe interest even a smaller group of people. They don’t rust at least. However, they will chip pretty easy. For those of us that have allowed ourselves to catch tektite fever there seems to always be room for one more on a shelf.