Abstract

Paper

WHAT ARE TEKTITES?

        The word tektite comes from the Greek word tektos meaning ëmoltení or ëmeltedí. Tektites are found together in large areas know as strewn-fields. There are four or seven strewn-fields on earth. The largest is the Australasian, covering Australia, Tasmania, Indonesia, and South Asia. It is estimated to cover almost 20 million square miles. Then there are the Czechoslovakian and the Ivory Coast Strewn Fields. The North American Field covers Texas, Georgia, Marthaís Vineyard, and Cuba.  Beyond these four majors strewn-fields there are also the Libyan Desert, Irgiz (north of the Aral Sea), and the Aouelloul (Mauritania, West Africa) Strewn Fields.
There have been many different theories on how these tektite strewn-fields came to be in existence. Today the most widely accepted version is that they are caused by impacts from large asteroid or comet impacts. They are thought to be the ësplashí or ëejectaí that is blasted up into space through the atmosphere and then falls back to earth. Not every strewn-field has a corresponding impact crater though. The Australasian field, on the other hand, may have several source craters. There are also many craters that do not have any tektites at all associated with them.
        They superficially resemble obsidian. They can range in color through black, brown, and bottle-green. In comparison to obsidian they have a much lower water and alkali content and have very distinct surface textures. There is an interesting experiment that can be done to illustrate the difference in water content between tektites and obsidian. When heated by a blowpipe, the water in the obsidian causes it to froth, while the tektite will simply melt. In general their chemical composition is similar to silica-enriched igneous and certain types of sedimentary rocks such as shale. Depending on the exact sample, tektites can range from 64-84% SiO2.
           Tektites can range in size from pieces that are a few millimeters across and are roughly walnut sized to about 20 cm, the size of an apple. They generally only weigh a few grams, but the largest one recovered had a mass of 12.8 kilograms. They can be classified into three main forms. Splash forms look like solidified drops of liquid. They can appear as spheres, teardrops, dumbbells, and disks, and are the most common of the three. Ablated forms are modified splash forms that have been altered by heating and rapid acceleration on its fall back to earth. The front part looks like a shield and has a smooth polished surface. As a tektite falls through the atmosphere, compression heats up and melts the forward surface. This material from the heated side then flows up to form a ridge or flange. The rear keeps the shape of a splash form. The third major type is the Muong Nong form. They are chunks of tektite with a layered structure.
        Tektites have many unusual surface features. Many are pitted, have furrows or groves, or have fine striations. Some of these features are the result of etching while on earth, others are the result of the stresses of falling through the atmosphere to the earth. Many tektites show sighs of flow structures and layering. Although the exact form that this takes is dependant on what kind of tektite it is; splash forms have layering that is quite distinct when compared to ablated and Muong Nong forms. Also present in most tektites are ëbubble cavitiesí. This is trapped gas that has a similar chemical composition to the current atmospheric values. It is basically air that was trapped inside the molten tektite material.
        Tektites can be purchased just like meteorites and are often less expensive. The price can range from about $1.00 to over $10.00 a gram depending on the rarity of the tektite. Unusual shapes, sculpturing, and color also affect their value. Beyond the western collectorsí commercial value, there are cultures in South East Asia and Australia who ascribe medical or magical powers to tektites. Evidence has also been found of prehistoric people using them for making arrowheads (Fiske ).

IMPACT ORIGIN THEORY

        The most probable theory as to the origins of tektites is that they were formed from impact. Tektites exist in strewn fields. Strewn fields are determined by the chemical compositions of the tektites found and how old they are. A tektite strewn field is by no means a compact area. The Australasian strewn field has tektites in Australia, southern China, the Philippines, Thailand and Indonesia. There are four major strewn fields, one in North America, the Ivory Coast, Czechoslovakian and Australia. There is also Libyan Irgiz, and Aouelloul, depending on what you read. Australia has the youngest strewn field just .7 million years old (Glass 397). The oldest tektite strewn field is right here in North America. Tektites from this strewn field have been found in Texas, Georgia and Marthaís Vineyard.
 One of the fist people to theorize that tektites were from impact was Virgil E. Barnes who was especially interested in tektites found for the first time in North America in Texas. Virgil noted that since Lechatelierite particles were found in these tektites therefore the fusion was fast, heat was high and the cooling was also fast. The most probable conclusion why was that there was rapid heating caused by meteorites fusing the soil upon striking the earth (Barnes 36).
         To prove this theory further, there are several elements found in Tektites that would seem to relate to a parent material. The Ni/Co, Fe/Ne, 87Sr/ 86Sr, deuterium/hydrogen and Pb isotopic ratios all would be most probable if referring to a terrestrial parent material (Glass 400). Also there is a strong line of reasoning that tektites are formed by impact melting and this goes back to Barnes. Lechatelierite particles, which are abundant in tektites, are commonly found in impact glasses but not in volcanic glasses. The shape of the particles are contorted and long, which are indicators that the Lechatelierite was once so hot (up to 2000 degrees C) that they were fluid. Since the particles are in such close contact with the glass, the heating must have been for a very short period of time. So they got hot really fast and then cooled. There are other compositions in the different strewn fields that show high temperature. Baddeleyite, present in North American tektites from Georgia. Cosite in some Muong Nong tektites (Barnes 401).
         The Bosumtwi crater is an excellent example when trying to promote the impact theory in relation to tektites. The Ivory Coast tektites exist within a 10.5 km diameter of the Bosumtwi crater. Also the Ivory Coast tektites are close in age and composition to the impact glasses from the Bosumtwi crater (Glass 403). All other relationships between a crater source and tektites are problematic due to lack of good source material for the Czechoslovakian tektites and no hard proof that the tektites from North America and Australia are associated with one crater in particular.
 

OTHER ORIGIN THEORIES

        Although most scientists now believe that tektites originate from impacts, many other theories have been expounded over the years.  These theories can basically be broken down into two categories: terrestrial origin theories and extra-terrestrial origin theories.  There is a great similarity between the chemical composition of tektites and terrestrial sediments. This has led many people to conclude that tektites are formed from terrestrial material that has been heated to an extraordinarily high temperature somewhere in the vicinity of 2000 degrees C.  Few earthly sources can produce such extreme temperatures. (Urey 28)
        Hawkins has argued that tektites are formed when lightening fuses surface soil. Although lightening produces high enough temperatures to do this, practical experiments have shown that when lightening fuses surface soil it creates small tubes and rods very unlike tektites.   It has also been argued that lightening causes tektites by fusing dust particles in the atmosphere, however there is no proof that lightening causes atmospheric dust to aggregate and fuse. In fact, Nininger has pointed out that, "thunderstorms accompanied by dust clouds are common in the Great Plains area of the U.S.A, yet no tektites have ever been found there." (Mason 219)
        Volcanic activity is another proposed source of terrestrial tektite formation.  A terrestrial volcanic origin theory is discredited, however, by the lack of similarity between volcanic glasses and tektites; and by the fact that, "no volcanoes are distributed in such a way as to produce their [tektites] observed distribution." (Mason 219)
        Two other terrestrial origin theories have been proposed, but they have been abandoned because they can in no way account for the composition or distribution of tektites.  These theories are: creation of tektites through natural fires such as forest fires, burning straw etc., and creation through human activity. (Mason 219)
        The major extraterrestrial origin theory is that tektites come from the moon, either from lunar volcanoes or from splashes of a meteoritic impact.  The lunar volcano theory is suspect because active volcanoes are thought to have last been seen on the moon somewhere in the realm of 100 million years ago, while many tektites show material much younger than that.  (Wert and Weller 54)
Similarly, evidence has been presented by Urey and others that it would be almost impossible for any splash material from the moon to be distributed on earth in the fashion that tektites are. (OíKeefe 97-98, 1959)   Although Varsavsky has found that, under certain conditions, materials falling from the moon might fall in a distribution similar to a strewn field; most people reject his calculations because they claim that any tektites which missed  the earth on the first encounter would go into orbit and eventually rain down all over the earth.  Thus, stray tektites should be found all over, which they are not.  Other critics of the lunar impact theory point out that tektitesí compositions are more similar to terrestrial matter than lunar matter. (OíKeefe 173, 1963)
        Other, less popular extraterrestrial theories include the idea that tektites are pieces of a planetary body with a glassy surface layer that has been disrupted, that they are themselves meteorites formed from free Si, Al, Mg etc., or that they are created from stony meteorites by fusion in earthís atmosphere. (Mason 220)
        Although it appears today that terrestrial impacts are the cause of tektites, one should remember that each of the above theories has been seriously proposed and explored at some point in the past, and no one knows what people will come up with in the future.
   

Cited References (& Database in which source material was identified)

Fiske, Peter. "Teketite Frequently Asked Questions" . website. The Layered Tektites of Southeast Asia: A Field Expedition supported by the National Geographic Society. http://www-phys.llnl.gov/tektite/faq.html. (google)

Glass, B.P. "Tektites and Microtektites: Key facts and Inferences." Tectonophysics. Vol.171, no. 1-4 (1990) p. 393-404. (INSPEC)

Mason, Brian. Meteorites. John Wiley and Sons, NY, 1962. Pg. 218-220 (OBIS)

Nininger, H.H, 1952: Out of the Sky. University of Denver Press, 336.  Quoted in: Mason, Brian. Meteorites. John Wiley and Sons, NY, 1962. Pg. 219 (OBIS)

O'Keefe, John A. "Origin of Tektites" Science, New Series. Vol. 130, No. 3367. (Jul. 10, 1959), pp. 97-98. (JSTOR)

O'íKeefe, John A. "The Origin of Tektites." In O'Keefe, Jon A., ed. Tektites. The University of Chicago Press, Chicago, 1963. (OBIS)

Poag, C. Wylie, Powars, david S., Poppe, Lawrence J., Mixon, Robert B. "Meteoroid Mayhem in Ole Virginny: Source of the North American tektite strewn field." Geology, v. 22, p.691-694, (August 1994) (GEOREF)

Urey, Harold C. "On the Origin of Tektites." Proceedings of the National Academy of Sciences of the United States of America.  Vol. 41, Issue 1 (Jan. 15, 1955), 27-31 (JSTOR)

Wert, C., Weller, M. "Internal friction of the glassy Tektites." Journal of Alloys and Compounds v. 310 p. 54-58. (JSTOR)