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Tektites are glass-like stones with pitted surfaces that come in various shapes and sizes, found in scattered fields across the world. They are believed to result from meteorite impacts that heat and pressurize soil and rocks, causing molten material to be ejected and scattered over a large area. Tektites have high silica content and are often named after the localities where they are found. Their shapes and chemical compositions strongly support the meteorite impact theory.
Tektites are smooth stones, usually dark in color, made of a glass-like material with a surface that appears to be pitted. The term comes from the Greek word teknos, which means “smelted”. These stones come in a variety of shapes and sizes and from a number of known places; radiometric and other dating methods place the dates of their formation between 35 million and 750,000 years ago, depending on location. They often resemble types of volcanic glass such as obsidian, but have distinctive characteristics that indicate a different origin. Over the years, various theories have been advanced about their formation, but it is now generally accepted that they result from the sudden heating and pressurization of soil and rocks caused by meteorite impacts.
There are several places on Earth where tektite stones are found; these are large areas over which objects are thinly scattered and are known as scattered fields. The largest of these locations covers most of Australasia and extends into Southeast Asia. The other major fields scattered are in North America – in Texas, Georgia and a few other locations; Czech Republic; and the Ivory Coast of Africa. Tektites also occur in some smaller areas; for example, a yellow or greenish form known as “desert glass” is found in the Libyan desert. Many types of these stones are named after the localities where they are found.
Tektites occur in a number of distinctive shapes and irregularly shaped masses, but can be divided into three main types. The Muong-Nong type – which takes its name from a city in Laos, in Southeast Asia – consists of irregular fragments, sometimes with a dish-like appearance. Splash-shaped types take on a variety of shapes, including spheres, teardrops, and dumbbells. The flanged button type has a circular shape with a ridge around it created by intense heating on one side.
Early researchers proposed various theories to explain tektites. Volcanic activity was a candidate; however, the structure and composition of these stones was found to be different from that of the material ejected from volcanoes. Rock or ground heated by lightning seemed like another possibility, but specimens of objects known to have been created this way, called fulgurites, exist and are completely different in appearance and structure; even lightning theory fails to explain the non-uniform distribution of the tektite. Some theorists have proposed that they were small meteorites or meteorite fragments; a variation on this theory is that they were ejected from the surface of the Moon by meteor impacts. Chemical analysis of meteorites and moon rocks, however, has disproved this theory as well.
However, it seems that the meteorite theories weren’t too far from the truth. A large meteorite impact on earth would heat surface soil or rock almost instantly to very high temperatures and subject it to enormous pressure, before ejecting large amounts of molten material and propelling it high into the atmosphere. Chunks of molten material would then fall back to the surface, scattered over a large area. Analysis of tektite shapes, structure and composition strongly supports this theory.
The shapes of tektites are generally consistent with airborne molten material, and the frequently observed pockmarked appearance suggests collisions with dust particles in the atmosphere. Spherical objects can be explained this way, with surface tension maintaining the shape. The shape of the dumbbell would result from a mass of molten material spinning in the air, with the material pulled towards both ends – and a broken dumbbell would produce the common teardrop shape. The shape of the flanged button can be explained by the fact that the molten material is pushed away from the downward direction of travel as the object falls back to the surface. The irregular plate-like shapes could originate in pools of molten rock near the impact site which would solidify into a tektite rock form.
The chemical compositions of tektites are notable for their high silica (SiO2) content, ranging from about 70% in Australian specimens to about 98% in desert glass. The remainder consists mainly of metal oxides. These materials all have very high melting and boiling points; the lack of volatile materials suggests they were subjected to intense heat. The presence of a mineral called lechatelierite, formed from silica subjected to great heat and pressure, in many tektites also supports the meteorite impact theory. In several cases, impact craters have been found that may be associated with tektite locations.
