Tektite Glass Research Articles

Crystalline inclusions in a Muong Nong-type indochinite

Zircon, corundum, rutile, monazite and quartz (identified by x-ray diffraction) have been recovered from a Muong Nong-type indochinite. X-ray asterism studies indicate that all of the minerals are shocked. The tektite glass surrounding the rutile crystals is a dark brown color rather than yellow-green like the rest of the glass, indicating that the rutile was starting to melt. The corundum appears to be a decomposition product of one of the Al 2SiO 5 minerals (kyanite, sillimanite or andalusite). The presence of an Al 2SiO 5 mineral strongly suggests a metamorphic component in the tektite parent material. The presence of zircon, rutile, monazite, chromite and quartz as well as an unknown aluminum silicate mineral in this and another Muong Nong-type tektite indicates that the tektites were produced from a detrital sedimentary material. The presence of these minerals in Muong Nong-type tektites seems to strengthen the case for a terrestrial origin for tektites.

Erasure of fission tracks in glasses and silicates by shock waves

Shock loading experiments have been carried out to determine the effect of dynamic pressures and associated temperatures on fission tracks in tektite (indochinite) and soda-lime glasses, biotite, and apatite. Below shock pressures of83 ± 4and31 ± 3kb, track densities remain unaltered in the tektite and soda-lime glass, respectively. In the tektite glass, partial and complete erasure of tracks is observed in samples recovered from112 ± 2and133 ± 10kb. In the soda-lime glass, partial erasure is observed in samples recovered from33 ± 3and42 ± 3kb. Shock temperature calculations indicate that the temperatures achieved upon shocking the glasses are appreciably lower than those at which tracks would be annealed out under static conditions. Single-crystals of apatite retain tracks when shocked to45 ± 5kb. apatite recovered from shock pressures above82 ± 5kb is granulated to micron-sized particles which preclude recognition of tracks. Single-crystal biotite specimens shocked to pressure up to173 ± 5kb show no appreciable loss in fission track density.

Chemical investigation of Australasian tektites

Chemical analysis of Australasian tektites inferring extraterrestrial igneous origin, noting similarity to preimpact parent rock

Magnetite bearing spherules in tektites

Black magnetic spherules, 30–150 μ in dia., extracted from crushed indochinites and other tektites, as well as magnetic fractions of various impact glasses were polished and studied under the reflecting microscope and by the electron microprobe. In the tektites, three kinds of spherules were found: type I, magnetic spherules consisting of magnetite skeletons embedded in a glass matrix with a small nucleus of pure iron; type II, intergrowths of magnetite and wüstite and some interstitial glass; and type III, a single glass spherule which contains finely distributed magnetite skeletons and idiomorphic magnetite crystals partially intergrown with wüstite. In impact glasses, magnetite does not occur in spherules but as type I (called primary magnetite), representing the more or less effected titanomagnetite of the original rock; and type II, intergrowths of glass and skeletal magnetite, in which iron and oxygen are the only constituents (interpreted as secondary and analogous to the magnetite spherules in tektites). The absence of nickel in the metallic phase and the lack of diffusion boundaries around the spherules in tektites is evidence that the spherules are not of meteoritic origin but formed within the tektite glass. The presence of skeletal magnetite in glass spherules indicates rapid cooling of a high temperature melt.

Infrared analysis of water in tektites and other glasses

Water content of tektites, impactites and artificial glass of tektite composition using IR absorption measurements

PLANETARY SCIENCE Devitrification of Tektite Glass

THEORIES of the origin of tektites have usually been based on the assumption that tektite glass is stable. In view of the critical nature of this assumption, the tendency of various natural tektite glasses to crystallize has been studied by subjecting them to heat treatments for specified lengths of time. Two types of experiments were performed, one involving the heat treatment of supercooled glass above the strain point, and the other, crystallization of tektite liquid on slow cooling from the melt. The tektite samples used in these experiments were lent by R. S. Clarke, jun., of the Smithsonian Institution, and E. C. T. Chao of the US Geological Survey.

External form and structure of some hollow australites

Thirteen hollow australites, 1.15–3.25 cm in diameter, range in weight from 0.717 to 12.539 g. Most are weathered by abrasion and/or by natural solution etching, but the internal cavity remains intact in each specimen. The volumes of the internal cavities range from 0.002 cm 3 in the smallest form, to 4.0 cm 3 in the largest form, and the specific gravity values of the hollow specimens range from 2.420 in the second smallest form to 1.357 in the largest form. Although specific gravity values generally decrease towards the larger, heavier specimens with their usually larger internal cavities, specimens in the 2.2–5.8 g weight range show slight departures from this trend according to the size of the internal cavity relative to the amount of enclosing tektite glass. Thus, specimens of similar weight and size do not always have internal cavities of similar size, and a somewhat larger specimen does not always have a larger internal cavity than a somewhat smaller specimen. To remain as unbroken hollow forms these specimens have survived the effects of aerodynamic heating at high speed entry through the earth's atmosphere, resisted breakage on impact, and withstood weathering by abrasion and terrestrial solution etching.

Vapor pressure of tektite glass and its bearing on tektite trajectories determined from aerodynamic analysis

Various experiments have been conducted to resolve a large discrepancy between two measurements that have been reported for the vapor pressure of tektite glass. This discrepancy significantly affects the trajectories and mode of tektite origin as determined from calculations of aerodynamic ablation. Measurements in a furnace of vaporization rate relative to that of four different standards (SiO2, TiO2, Au, Ag) yield mutually concordant results for tektite vapor pressure. Also, measurements in an arc jet of the stagnation temperature, the rate of surface recession, and the mass loss during aerodynamic ablation are in mutual agreement with the results from vaporization rate measurements. Further, observations of flash boiling occurring under certain experimental conditions, and not occurring under others, provide a bracketing of tektite vapor pressure that is also compatible with the other measurements. Over the temperature range of the present experiments, 1700 to 3000°K, a least-squares fit to the data is represented by Pν(atm) = exp[18.5 - 57,400/T(°K)]. These various experimental results demonstrate that previous measurements by other investigators of the pressure for incipient bubbling do not represent tektite vapor pressure but, instead, some bubble pressure that at certain temperatures is as much as a million times higher than the vapor pressure. Some recent aerodynamic calculations of very shallow, grazing tektite trajectories, which were based on bubble-pressure measurements, are therefore invalid; other calculations of relatively steep, direct-entry trajectories are not affected significantly by the new vapor-pressure data.

Devitrification of glass around collapsed babbles in tektites

Devitrification was first observed around partly collapsed bubbles (vacuoles) in Santa Mesa philippinites heated by the fire which destroyed Manila near the end of World War II. This localization of devitrification furnishes independent evidence that bubbles in normal tektites were formed by water vapor and that the very low pressure in normal tektite bubbles resulted from the absorption in or reaction of the water vapor with the surrounding tektite glass. Although tektites are essentially anhydrous they do contain a trace of water, in fact more than enough to form all the bubbles found in tektites. Experiments show that a similar amount of devitrification and partial collapse of bubbles takes place in philippinites when heated about 4 days at a temperature of 825°C. Under identical conditions of time and temperature australites, indochinites and javanites showed equivalent amounts of change in shorter times. Bediasites showed no change in 7 days. Neither collapse nor devitrification took place around bubbles in Muong Nong-type tektites, indicating that water vapor was not an important constituent of the gas forming these bubbles and that the pressure in the bubbles approaches equilibrium with atmospheric pressure.

Dumbbell Shaped Australite from Port Campbell, Victoria

AbstractA dumbbell shaped australite from Port Campbell, western Victoria, weighing a little over 5 grams and with a specific gravity of 2.381, possesses two gibbosities of unequal size and remnants of a circumferential flange with the same width in the waist regions as around the two unequal gibbosities.The anterior surface that faced down the flight path during high speed entry through the earth's atmosphere shows an unusual series of flow ridges in the aerodynamic sculpture pattern that extends from the stagnation point region of the larger gibbosity, across the waist region, and across the smaller gibbosity to its distal end. Such a series of flow ridges indicates that the trim of the dumbbell of tektite glass was generally broadside‐on, but with the front pole of the larger gibbosity somewhat in advance of that of the smaller gibbosity, so that the long axis of the form was at a small angle to the normal to the flight path direction.

Electrical resistivity and viscosity of tektite glass

The electrical resistivity of 25 tektites from seven different strewn fields has been measured as a function of temperature from 330–450°K by a time of discharge technique. From these data the activation energy for each specimen has been determined. It is shown that by using an equation similar to that found empirically by Littleton a viscosity curve between 1370 and 1770°K can be constructed. The calculated curve agrees within the limits of error with the experimental curves for several cases. The method can be used to calculate the viscosity within half an order of magnitude of the correct value. Mean viscosity curves are constructed from the experimental data for tektites from the seven known strewn fields.

Effects of temperature, pressure, and ionization of the formation and stability of fission tracks in minerals and glasses

In view of the demonstrated usefulness of the fission-fragment-track technique in geochronology, the effect of various geophysical variables on track formation and stability has been studied. Track fading in tektite glass, zircon, olivine, muscovite, phlogopite, and biotite was studied as a function of temperature, pressure, plastic deformation, and highly ionizing radiation. Temperature was found to be the most important parameter, and track-annealing data are given for each material. Hydrostatic pressures up to 80 kb have practically no effect on annealing curves of zircon and olivine. Track annealing in tektites can be accelerated only upon application of an hydrostatic pressure much larger than would ever be encountered by even a well-buried tektite. Purely hydrostatic pressures do not accelerate track annealing in micas, but shear deformations can shorten, distort, or erase tracks. Large doses of ionizing radiation (other than extremely massive nuclear particles) have no effect on track stability in any of the materials. Tracks formed at 77°K have the same appearance as tracks formed at room temperature or higher.

New data on the nickel-iron spherules from Southeast Asian tektites and their implications

This paper presents new occurrences and mineralogic, petrographic, and chemical data on metallic spherules found in Philippine tektites from the Ortigas site of Mandaluyong near Manila and in indochinites from Dalat, South Viet Nam. Most of the metallic spherules contain kamacite, schreibersite and troilite. Schreibersite and troilite occur interstitially or in blebs among round or elongate fine-grained matrix kamacite. Where abundant, schreibersite coalesces and forms a network throughout the entire spherule. Troilite generally occurs in small round droplets within the schreibersite. The amount of schreibersite varies from less than 5 to about 35 per cent by volume and the troilite may constitute as much as 5 per cent of the spherules. The composition of the phases present in the spherules was determined by the electron probe. In 9 analysed spherules from philippinites of the Ortigas site, the kamacite ranges from 1.6 to 4.5 per cent nickel. The average nickel content of kamacite in 3 analysed spherules from indochinites ranges from 4.7 to 12.9 per cent. The average nickel content in 4 schreibersite grains analysed from a single spherule ranges from 12.1 to 15.8 per cent. The spherules in the tektites are nearly identical with the meteoritic spheroids from Meteor Crater, Arizona, in texture, mineral assemblage and nickel content as shown by the new data. We conclude that these spherules were formed as molten droplets of an impacting meteoritic body which was instrumental in producing the tektite glass.

Experimental testing of hypotheses for the origin of tektites

A letter to Nature by Cassidy and Segnit (1955) reported the finding of highly siliceous spheres of glass embedded in glass of more basic composition in high-temperature quench runs made on tektite material. On this basis it was suggested that the “lechatelierite” inclusions in tektites represent a siliceous glass immiscible with the main body of more basic tektite glass. Work reported here contradicts the earlier results. Two quench samples are illustrated in which appear features looking remarkably like liquid-liquid equilibria. The earlier misrepresentation is attributed to one of these. A paper by Cassidy (1958) suggested a common origin for tektites and stony meteorites through segregation by liquid immiscibility. Experimental work reported in the present paper do not support this hypothesis, and it is discarded. The liquidus temperature of a natural australite was found to be 1347 ± 15° C and its primary crystalline phase was found to be SiO 2 (cristobalite). From this it is concluded that tektites are not igneous products derived from more basic rocks by the well-known process of crystal fractionation. They could have been formed by melting of sediments of the requisite composition or in a magma that had become highly siliceous by incorporation of appropriate xenolithic material.

On the unity and origin of the Australasian tektites

Aerodynamic experiments with tektite glass demonstrate that, subsequent to the termination of ablation, high thermal stresses are formed within a thin outer shell. This shell spontaneously spalls, leaving a core shaped like many of the tektites found in Billiton, Java, Philippines and Australia. Certain tektite fragments from Java and Australia are shown to have the same internal stress patterns as pieces of aerothermal stress shell. The over-all evidence indicates that the Australasian tektites descended into the atmosphere as rigid objects of glass. Core shapes found in the extreme southwest part of Australia surprisingly are more like those found in the Philippines than in other areas of Australia; comparisons of chemical analyses and of specific gravity population polygons reveal the same striking circumstances. It is concluded that all Australasian tektites represent a single event. A study of tektite forms, in relation to results from laboratory experiments, indicates that the temperature of formation of primary shapes varied progressively across the Australasian strewnfield. The sculpture on certain australites provides a record of tumbling during entry into the Earth's atmosphere. The effect of turning on the determination of entry trajectories is discussed, and new evidence is presented pertaining to the deceleration which existed when ablation terminated on the australites. The trajectory determinations correspond to an origin from the Moon. Numerous trajectories from the Moon to Earth have been studied with a high-speed electronic digital computer. The relative probability of such trajectories is about 1 200 for the Moon as a whole, and 1 60 for certain crater locations. A comparison of the geographical spread of the Australasian tektites with the Earth landing patterns for lunar material ejected within the a zimuthal dispersion observed of lunar rays, and within the elevational dispersion measured in hypervelocity impact experiments, indicates mutual compatibility.

On the lunar origin of tektites

The experimental facilities and analytical methods of atmosphere entry aerodynamics have been applied to the study of tektites. Hypervelocity ablation experiments in the laboratory have reproduced the same surface sculptures, geometric relationships, systematic stria distortions, and coiled circumferential flanges as those found on tektites from Australia, The aerodynamic evidence demonstrates that the javanites and australites were twice melted, the second time by aerodynamic heating of rigid tektite glass during atmosphere entry. Experiments conducted on molten glass ejected into the atmosphere at various viscosities and velocities show that the primary australites were formed in an environment in which the atmosphere density was many orders of magnitude less than that at the earth's surface; this contradicts the hypothesis of tektite origin from the earth or other atmosphere-shrouded planets. Modern calculation methods for aerodynamic ablation are shown to be in good agreement with various laboratory experiments and with an entry flight experiment. From the amount of ablation, the distortion of striae, and the spacing between ring waves on australites, entry trajectories have been determined. The moon is the only known celestial body of origin compatible with these trajectories. The distribution of chemical elements in tektites, earth crust, meteorites, and other cosmic bodies is compared, and a brief discussion is given of the chemical differentiation of the lunar crust to which the over-all evidence points.

A perfectly developed hollow australite

Reexamination of a hollow australite from western Victoria shows that it resulted from ablation of a sphere of tektite glass containing an elliptical internal cavity. During fall only the exterior glass was subjected to ablation, and the original hollow persisted.

Rare gases in tektites

Tektites from a number of localities have been examined for their contents of potassium, atmospheric argon, radiogenic argon, atmospheric neon, and possible cosmogenic neon. At 300°K, the coefficient of diffusion for helium in tektite glass from Kalgoorlie, Australia is 4 × 10 −10 cm 2/sec. The activation energy for helium diffusion is 0.27 electron volts. The helium solubility constant is 0.005. Corresponding quantities for neon diffusion are 2 × 10 −15 cm 2/sec, 0.61 electron volts and 0.005. The helium diffusion rate is so high that tektites retain no radiogenic or cosmogenic helium. The recent group of tektites, however, should retain a substantial amount of any cosmogenic neon contained at time of fall. In no case was any excess Ne 21 detected. From the upper limits of original Ne 21 content, a maximum “flight time” since last melting has been computed for each tektite. For a tektite from Kalgoorlie, this is 28,000 years. This result is in apparent disagreement with the finding by Ehmann and Kohman of radioactive Al 26 in australites. Potassium-argon ages have been computed for each tektite. These range from 0 to 32 m.y. and are usually in agreement with the stratigraphie age of the formations on which the tektites lie, according to presently accepted time scales. Data in this paper do not support a recent suggestion that the moldavites of Czechoslovakia and the recently discovered tektites from Georgia U.S.A. are part of the same fall.

Origin of Tektites

— The origin of tektites has been obscure because of the following dilemma. The application of physical principles to the data available on tektites points strongly to origin from one or more lunar volcanoes; but few glasses of tektite composition have hitherto been reported from the lunar samples. Instead, the lunar silicic glasses consist chiefly of a material very rich in K2O and poor in MgO. The ratio of K2O/MgO is higher in these glasses than in any tektites reported. The solution of the dilemma seems to come from the study of some recently discovered terrestrial deposits of tektite glass with high values of K2O/MgO at the Cretaceous-Tertiary boundary. These glasses are found to be very vulnerable to crystallization into sandine or to alteration to smectite. These end products are known and are more abundant than any terrestrial deposits of tektite glass. It seems possible that, in fact, the moon produces tektite glass, mostly of the high K2O-low MgO type; but on Earth these deposits are destroyed. The much less abundant deposits with lower K and higher Mg are observed because they survive. Other objections to the lunar origin hypothesis appear to be answerable.