Tektites

Abstract

Tektites are small, generally rounded, silicate glass bodies found in several widely separated areas of the Earth's surface called strewn fields. Four strewn fields are recognized: (1) Australasian, (2) Ivory Coast, (3) Czechoslovakian, and (4) North American. Tektites from the four known strewn fields were formed approximately 0.7, 1, 15 and 35 million years (m.y.) ago, respectively. Tektites are generally black, but those from Czechoslovakia and Georgia are translucent green or brown in color. Most tektites occur as splash forms, but some are blocky with a layered structure (Muong Nong-type); and some of the splash forms have been remelted or ablated by high velocity flight down through the Earth's atmosphere. Although they superficially resemble obsidian, they can be distinguished from obsidian by their petrography and compositions. Tektites, unlike obsidians, contain ubiquitous lechatelierite (SiO2 glass) particles and are generally completely devoid of microlites or crystallites. Tektites are drier than obsidians and have higher FeO/Fe2O3 ratios. Although some researchers favor a lunar volcanic origin for tektites, most of the chemical, isotopic, and petrographic studies seem to support a terrestrial impact origin. The presence of lechatelierite, coesite, shock relict inclusions, and Ni-Fe spherules favors an impact origin; and chemical and isotopic data indicate that the parent material was a terrestrial sedimentary deposit. The Czechoslovakian and Ivory Coast tektites have been associated with the Ries crater (in Germany) and the Bosumtwi crater (in Ghana), respectively.