Tektites, in the simplest terms are pieces of natural glass. Several natural glass types are found on the Earth. By outward appearance some tektites resemble obsidian the commonest of the natural glasses. Microscopically, tektites resemble glass more than obsidian in that they are almost completely devoid of any mineral crystals in their composition. The tektite glass is homogeneous in nature with the elements it contains dissolved and mixed. Tektites have much less water in their composition than obsidians (often a thousand times less). Also obsidians when heated will foam from the gases and water they contain and this is one method of tektite testing. At the same temperature tektite glass may produce a few gentle bubbles. Tektites are made of a glass which melts at a far higher temperature and it is far more viscous.Where did tektites come from? There have been several schools of thought over the last hundred years, but basically today it distills down to the Earth through the impact of a meteorite or comet.
In a cratering event, soil and rock are liquefied, or vaporized. There is question as to how long the tektites took to form and how high they were ejected. Was it a simple trajectory or did they travel high nearly into space? It is clear that part of the time they traveled at very high speed for they had to traverse great distances. The Australasian strewnfield is thousands of kilometers across. It is thought by impact theorists that they are shaped in a plastic state as they spin. Later there may be some mostly minor shaping by ablation. In regard to the Australites, it is clear from cross sectional analysis that they are a remelted object. Unlike the other tektites they received a major part of their final shape by ablation. However, the button portion of the posterior side has internal flow lines unchanged by remelting while those on the incoming ablated side are turned an pulled. Clearly, the internal structure was established and set, before the hypersonic ablation in the atmosphere.Current chemical analysis of tektites indicates that there is a relationship to rocks only found on Earth. Fifteen rare earth elements have been used to show that their relative abundances are in exact relationship to their abundance in tektites. Including an anomaly in the amount of Europium. This depletion of Europium is connected to calcium and CO2 chemistry on the Earth. This depletion is exactly recorded in tektite glass. Melting a granite like rock will essentially make tektite glass composition. Oversimplification but actually close since many sedimentary rock thought to be used for tektites are derived from granites.
Tektites are found sometimes as irregular blobs and angular fragments, but often they are clearly a splash form of one type or another. These splash forms include, spheres, discs, rods, teardrops, dumbbells, and varieties of all these with bending and slumping. Some of the forms listed are clearly a result of the exaggeration of the cause processes of another form. For example teardrops are by all appearances the result of the continued separation of the bulbed ends of dumbbells which have become too thin in the middle to stay connected. Careful examination of the thin pointed end of an undamaged teardrop will reveal that it has the same fine texture as the rest of the piece and is not the result of breakage. It has become a complete individual. The discs will often have a cavity in the middle of each side causing them to be thinner in cross section in the middle. On a much smaller percentage of the discs there will be a peak where they have also spun off of another portion.
Spheres may have a smooth surface or the pieces may be deeply grooved. The spheres are also amongst the most stressed of the tektites often shattering into dozens of pieces when an attempt is made to cut tektites. Besides nearly perfect spheres they occur in the whole spectrum of flatten and elongated round forms.
The dumbbells as the name implies have knobs at each end connected by a middle which is thinner. The rod forms are similar to the dumbbells in size but have neither the thick knobs nor the thinner middle. They are just rods with usually rounded ends.
Some of these forms will show a slight ridge on occasion indicating ablation, but the Australites are the real aerodynamic shaped tektites. In their case ablation has done much to give them their form. Australite buttons have a hemispherical side often showing a spiraling raised 
line. The technical name for this is "ring wave'' it is a featured created as the surface melted, partly burned away, and partly re-deposited in the flange. The flange of Australite buttons is a ring of material around the original core that builds up but does not completely weld itself to the original mass. On occasion the entire forward facing side and flange will detach leaving a distinctive core. These flangless cores are found also. Australites come in elongated forms as well as round.Tektites come in many sizes however, complete splashform types fall in the range of from one inch to four inches. Their weight in the 10 to 100 gram range. (Please excuse the generalizations, this is for the readers who have not seen them and have no idea of the exceptions that the tektite enthusiast will be familiar with.) They can be much smaller and much larger than the figures above, but for a simple average the range given may be useful.
Tektites are not usually smooth, they are usually pitted or 
grooved or a combination of both. More often than not they have a bald spot which is smooth. Many attempts have been made to explain the pitting. It has been thought to be from exposure to chemicals in the ground. Another explanation is that it is part of their form received before landing, perhaps during flight in the atmosphere. The inside of broken bubbles will often be shinny showing almost no etching, yet it has been exposed to the same chemicals for the entire time the tektite has been on earth. The back un-ablated side of Australites will often be textured and old looking while the ablated front surface and both surfaces of the flange will appear very fresh. Again the time spent in the ground was of course the same. The mechanism of texturing may be a process called spallation. Pieces of glass pop out of the surface coming through the atmosphere. Some experimentation has confirmed this as a possibility.
grooved or a combination of both. More often than not they have a bald spot which is smooth. Many attempts have been made to explain the pitting. It has been thought to be from exposure to chemicals in the ground. Another explanation is that it is part of their form received before landing, perhaps during flight in the atmosphere. The inside of broken bubbles will often be shinny showing almost no etching, yet it has been exposed to the same chemicals for the entire time the tektite has been on earth. The back un-ablated side of Australites will often be textured and old looking while the ablated front surface and both surfaces of the flange will appear very fresh. Again the time spent in the ground was of course the same. The mechanism of texturing may be a process called spallation. Pieces of glass pop out of the surface coming through the atmosphere. Some experimentation has confirmed this as a possibility.Tektites have been found with other artifacts in archaeological sites dating back thousands of years. They have a long history of use and significance to man. Ancient man in many places took advantage of the glassy nature of tektites and used them for making flaked tools. Later, they were considered to have religious significance in Asia, the colorful green varieties (Moldavites) of Europe have been used for jewelry for hundreds of years and are making a return as gems today.
Tektites are not found everywhere on the Earth. They are found in strewnfields; which are areas where the material has fallen upon the ground and the material is confined to the boundaries of the strewnfield. Tektites are found more or less randomly within the strewnfield. In the case of meteorite strewnfields the heavier fragments will be found at the farthest travel end of the dispersion ellipse.
In addition to the large forms found on the land, microtektites are recovered in cores of sediments taken from the oceans. This data helps to define the boundaries of the strewnfields in the areas covered by ocean waters.
There are four well established strewnfields on the Earth and some other locations where tektite glass or very similar glass is found. The strewnfields are the North American (Georgia and Bediasite Tektites), The Moldavite, which is really two small strewnfield close to each other in Europe, The Ivory Coast, and The Australasian.
Debate continues as to whether tektites are found on the same spot where they fell, or whether they have been transported. Many scientists insist that they are found close to where they fell because studies indicate being glass they break very fast in a river or stream or flood situation. Others strive to prove that they have been worked from other strata and redeposited.It is however clear in some cases that they are found in essentially the spot they fell and in a specific layer or horizon in the ground.
by The Meteorite Exchange, Inc : http://www.meteorite.com/
