They can be mistaken for obsidian or pitchstone black volcanic glasses , but these will emit some water on strong heating. With a hardness of on Moh's scale, tektites will easily scratch window glass. They have a density range of 2.
This is a little lighter than quartz beach sand. Human built objects can be mistaken for tektites, particularly molten bottle glass, glass marbles, and black buttons. Many of these will not have the correctly-shaped rims, symmetrical structures or colours of real tektites, while others will be too heavy or too light.
The streamlined shapes of many tektites suggest a rapid movement through the atmosphere under low gravity conditions, with melting early in their formation. About 30 distinctly different shapes have been described. They start as a molten blob projected through our atmosphere, then 'freeze' into a shape as they solidify. The shape depends on whether the initial molten blob was rotating, and the speed of rotation.
The spherical and button types common in Australites had no or very little rotation with a fairly steady flight path direction. Their rear surfaces were more protected from heat, but the front surface, facing the flight direction, melted and was pushed towards the rear, piling up to form ridges and a rim or flange. These 'flanged button' shapes have been copied artificially at the Corning Glass Company in America, where molten glass spheres were placed in the jetstream of a wind tunnel.
The tear-drop shapes formed from stretching and breaking apart of rapidly rotating, elongated dumb-bells. Flat disks, ovals and boomerang shapes have all been found. After falling back to Earth as showers of glass, many tektites lay exposed to weathering and erosion at the surface or shallow depth. Many thousands of Australites have been washed into shallow lakes or depressions and are now found on claypans, and shallow drainage depressions. Effects of high temperatures, wind, rainfall and chemical attack have produced various types of surface etching or corrosion - pits, furrows, grooves or 'saw-cuts'.
Many Australites lose their rims under these conditions and become rimless cores. There is a strange corroded, layered type, the Muong Nong from Laos, south-east Asia, which forms masses up to 24 kg and may have melted only at the Earth's surface rather than being projected up into its atmosphere and melting again on re-entry. There is no record of anyone having ever witnessed the fall of a tektite, and their formation may depend on the very infrequent arrival of large meteorites or asteroids which would cause great devastation if they came today.
There have been many theories for tektite origins, with a lunar origin rock splashed out from the moon by meteorite impact, or erupted from volcanoes being dismissed only recently. The most favoured theory suggests an origin from Earth, where rock was hurled up into our atmosphere by the impact of a large meteorite or asteroid, then partially re-melted as it fell back through the atmosphere to the ground.
In this theory's favour is the chemical similarity between some Earth rocks and tektites, and the composition of gas bubbles in Moldavites. The gas in these bubbles was under very low pressure, equivalent to 32 km altitude in our atmosphere.
The idea that natural fires such as forest fires or ground fires igniting coal seams could be a source of tektites. Although these fires may reach very high temperatures, the presence of ablation shapes and other unique chemical properties in tektites discounted this theory.
Another proposed alternative for tektite formation was the fusing of silica-rich surface soil and dust by lightning. These forms, called fulgurites, while having attained high enough temperatures to have melted the silica, do not have the same appearance as tektites, often occurring as soda-straw shaped tubes, as seen here, and possess none of the unique chemical and physical properties that set tektites apart from other naturally occurring glasses.
In addition, the nature and scale of tektite occurrence discounts this theory as well. Lightning strikes occur thousands of times each day. If this theory held true, tektites would be found throughout the world, in great abundance. After the Apollo Moon landings scientists studied and compared the chemical composition of lunar rocks to tektites.
Their conclusions showed that there was little to no similarity between tektites and lunar materials, shedding doubt on the lunar origin of tektites, and adding credit to the terrestrial impact theory that is now widely accepted. The main issues facing both past and current scientists working with tektites is the determination of when, where, and how they originated.
To deduce the conditions necessary to produce tektites, it is important to recognize several significant properties about tektites. These properties include:. Tektites are distributed across the Earth in areas called strewnfields.
These strewnfields are found on every continent except Antarctica. Each strewn-field is comprised of specimens similar in age and chemical compositions, including tektites found on land, as well as microtektites, found in deep sea sediments, and are inferred to have been created by an impact event of the same age.
See images of possible tektite source craters. Others, named after the region or country in which they are found, include australites, javanites, indochinites, and philippinites. A few groups, such as the Ivory Coast tektites and Georgia tektites, are not specifically named. The ages of tektites are derived by several means. The age of ablation caused by atmospheric entry or re-entry can be derived by potassium-argon decay measurements. Fission track analysis, another geochronolgic tool, can indicate the latest heating episode of the tektite glass.
Tektites range in age from Using these dates scientists have tried to correlate the ages of tektite strewnfields with impact craters across the globe. For the most part, these researchers have been successful in determining the source craters for tektites, however, the source crater for the Australasian strewnfield, still has not been found, allowing some people to still question the meteorite impact theory.
Physical properties and chemical composition set tektites apart from other naturally occurring glasses. Normally the first thing mentioned about tektites is their color.
Outwardly, tektites appear to be glossy-black, but thin sections of specimens are translucent, and generally appear to be yellowish brown. The black color of most tektites can vary, however, depending on the strewnfield the tektite is located in. Moldavites are dark green and Libyan Desert glass is greenish-yellow to straw yellow in color.
Silica is the most common chemical constituent of tektites. What about tektites reported to be found in Tibet? Age Paradox Australites have been dated at , years by two radiometric dating methods - fission track and potassium-argon K-Ar.
Geologists however, from first hand field observations, place the fall at a much younger age. It is generally accepted though that the australites have not travelled far from where they landed and that the ones found on the surface in good condition have only recently been eroded out of certain 'paleosols'. These paleosols seem to be a lot younger than they should be if it is assumed that the tektites originally fell onto them.
The easy solution is to suggest that the tektites originally fell into older sediments but have since been washed out into these younger sediments! This improbable 'redeposition' has supposedly taken place over huge, widely separated areas in Australia and also in other tektite localities around the world! There is obviously something wrong with either the dating of the age of the tektites or the dating of the paleosols they are found in.
The dating of the flanges of buttons is similar to the dating of the primary body so it cannot be suggested that they were created at one time but fell only recently. Numerous samples of this paleosol were dated using the radiocarbon method at being between 24, and 16, years old. The nearest older deposits were 15 to 25 km away and it was inconceivable that the many delicately shaped fragile australites could have been transported that far without abrasion. They also found m of Quaternary deposits beneath the Motpena strewn field.
If the australites had fallen onto the plain in the early Pleistocene about In fact there was clear evidence that the tektites were eroding out of the relic sand dunes and being incorporated in alluvial and aeolian deposits of mid - Holocene age in the interdune corridors. The report concludes that:"No one who has seen the Port Cambell localities and examined the many perfectly preserved australites therefrom is likely to argue that these specimens are not being found essentially where they fell.
The complete lack of solution etching , even on thin plates weighing as little as 0. Cleverly of the School of Mines Kalgoorlie wrote about a patch of extremely well preserved tektites found near Kalgoorlie, many of which were of the rare, fragile form: 'It is still difficult to believe that small australites could have remained in such an area for the hundreds of thousands of years of 'age on earth' required by some authors; indeed, during even the modest periods of the order of one to tens of thousands of years advocated by the other school of thought, their situation must have been precarious.
The earlier noted scientists such as Charles Fenner, George Baker and Edmund Gill who picked up pristine tektites from the arid surface of Australia, became convinced that the shower of tektites arrived recently.
More recently Izokh in Vietnam found the age of fall to be Another Tektite Fall in Australia? A dozen australites high in sodium, were found in North West of South Australia which gave dates of 4 million years old.
Very little mention is found of this group and it seems hard to believe that a different fall of aerodynamically shaped tektites which are unique to Australia should occur in the middle of the general strewn field. Could there have been some errors with the dating of these tektites? Why have there not been more found? There does not seem to be much in the way of authentic records of new tektite falls.
A fall was witnessed in Igast , Latvia in but I have no information on it. There have been several reported sitings of 'fresh falls' in Australia but most are unconvincing. One explanation I can think of is that it was picked up somewhere by a very strong 'whirly wind' and later fell to earth again. This has happened with other objects. They heard a hissing noise and something flew past them like shrapnel hitting the ground with an audible thud.
They found a hole in the ground about 12 inches deep with the australite at the bottom. It was a typical ellipsoidal australite weighing 31 grams with a brilliant fresh looking black surface, sculptured with many sharply defined grooves and pits.
Unfortunately it was in the possession of Mrs G. Dewar who took it to Scotland to give to her brother. Hanson was working on a gravel tennis court when he heard a thud on the surface of the tennis court.
He found evidence of something having penetrated the surface and dug down to find a tektite, it was still too hot to hold in the hand! It was not until after showing it to numerous friends, that it was recognised as a tektite and handed to the West Australian Museum. It was a typical australite of specific gravity 2. It had the distinct equatorial rim.
There was no sign of weathering or sand abrasion on the very fresh shiny surface which had many typical grooves, minute wrinkles and pits. See below images. Only when such tektites are properly analysed and dated can a 'fresh fall' be authenticated. I have heard of 'fresh looking' australites being found in places where they were not seen before and being coated in a red substance which easily washes off in the slightest dew leaving a red rim around the tektite on the ground.
As the red substance has not been analysed or such tektites dated, the story can be considered only hear-say! The next day it was taken to the National Science museum and analysed. Internally it was found to resemble obsidian more than tektite.
It had numerous globular-shaped, irregular hair-shaped, opaque crystallites and colourless microlites. The flow structure was different to a tektite. It also contained numerous magnetite grains accompanied by partly reduced metals. In fact it contained five different types of iron including metallic iron in a silicate matrix.
It was found to be most similar chemically to terrestrial granite or lunar glasses but definitely had an extraterrestrial origin which was not too far from earth. They made some comparisons with tektites they obtained from the British Museum.
When you actually go searching for australites and start finding them if you are very lucky! Most of the dense patches have now gone but it was not uncommon in the past to come upon a small area of only a couple of acres which contained hundreds of tektites, yet identical surrounding country would have none at all!
Some of these patches could be due to erosional processes concentrating the tektites but in many cases the tektites are in too good a condition to have travelled far. In some salt lakes the tektites are found only in certain places near the edge. Either water action or wave action combined with wind has concentrated them up to one end of the lake like shells on a beach , or they are eroding out of old soils on the edge of the lake. From my own observations it seems that they are eroding out of ancient sand dunes along the edges of the lakes but only in isolated patches.
In the case of Port Campbell, they are eroding out of a certain old soil layer close to the cliffs but also out of the same shallow layer further inland where the ground has been disturbed or eroded away indicating a region of dense australites extending north west but only showing where surface erosion has taken place. It can only be imagined how many thousands still lie buried in shallow deposits. In the Map shown below australite distribution taken from the book 'tektites' written by Ken McNamara and Alex Bevan , I have superimposed what I believe to be bands of 'dense patches'.
The most striking of these bands of 'dense patches' is that of f - g ; which traversed some of the most famous and dense australite localities. If this line is continued to the north west it will be found to go directly to Indochina and the locality of the Muong Nong tektites and passes very close to the suspect impact crater of Tonle Sap! This is surely no coincidence. The other lines may also point to Indochina but at this stage I require more detailed information on localities of 'dense patches' for the Eastern Goldfields of West Australia rather than distribution of scattered tektites.
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