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Tektites are natural glasses that occur on earth in four distinct strewn fields (North American, Central European, Ivory Coast, and Australasian). Geochemical arguments have shown that tektites have been derived by hypervelocity impact melting from terrestrial upper crustal rocks, most likely sediments. The contents of Be-10 in tektites are evidence for a derivation of tektites from surface rocks, thus precluding an origin from greater depth in the crater. For two of the four tektite strewn fields (Ivory Coast, Central European), a possible connection to impact craters (Bosumtwi, and Ries, respectively) has been suggested on the basis of chemical, isotopic, and age data. No clear crater identifications have been made for the North American or Australasian strewn fields, although there are good candidates for both. Even though the geochemistry of tektites is in unequivocal favor of an origin by impact melting of terrestrial rocks, the unambiguous demonstration of the presence of an extraterrestrial contribution to the chemistry of tektites remains a problem. However, recent osmium isotope studies have shown that there is a clear meteoritic signature in at least some tektites. The exact mechanism of tektite formation is still not obv3ious, although some facts become increasingly clear. Tektite production requires specific impact conditions—otherwise there would be many more tektite strewn fields connected to the 150 or so known impact craters. Tektites are produced by nonequilibrium shock melting of surficial rocks, and the superheated melt may be subjected to a plasma phase during which they are subjected to partial reduction. They are then lofted through the atmosphere (probably in the wake of the expanding vapor cloud), quenched, and distributed over a geographically extended area—the strewn field. Some tektites solidify in a near-vacuum and re-enter the atmosphere. During the re-entry they melt again and form ablation-shaped tektites. Larger tektites, from a lower part of the target stratigraphy, are only distributed closer to the source crater. Many of them are more inhomogeneous melts and show a layered structure; they are called Muong Nong–type tektites. The study of tektites and the identification of possible new strewn fields provide important contributions toward the understanding of impact cratering.

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