Tektites 

by Bill Baird

The first mention of tektites in scientific literature describes them as a form of volcanic glass. Those who believed in their volcanic origins included Darwin, who compared australite buttons to volcanic bombs. Some speculated that they were the products of prehistoric glass manufacture or from the burning coal seams. Others considered that they might have been either ejected from volcanoes on the moon or a kind of meteorite or aerial fulgurites caused by lightning fusion during dust storms or desiccation of silicate gel masses. 

It is now generally accepted that tektites are the result of some kind of impact on Earth by meteorites or comets. However, searches made in relation to the Tunguska event, now generally believed to have been a comet airburst, have not yet found any tektite type material. 

Work on the isotopic composition of argon (Ar) in bubbles from gas-rich, splash-form tektites (Muong Nong type tektites) and Darwin glass, has revealed an atmospheric origin for this gas. 

Most tektites are about the size of a walnut, but range from much smaller specimens to blocky lumps up to 12.8 kg in weight. They are generally black in appearance, but when held to the light some are translucent. Those recovered in Czechoslovakia are often a beautiful clear light green in colour (faceted gems have been cut from moldavites up to 25 carats in weight), while those from the Libyan Desert are generally of greenish yellow. Tektites which appear opaque in whole specimens may be translucent or yellowish brown in thin plates. 

In form they may be the shape of a teardrop, dumbbell, rod, sphere, disc or flanged button. Often the original is modified by spalling, breaking or etching. A special type of blocky, layered tektite was first described from Muong Nong, Laos. 

Tektites are found from over a large part of the world, occurring as strewn fields but within defineable areas. Each group appears to be associated with specific, but widely separated arrival events, with no evidence for inter-group activity. These groupings vary in age from around 15 thousand years for those in Australia, to 40 million years for North American tektites. 

Tektite from specific occurrences have usually been assigned distinctive names. For example those found in Czechoslovakia are termed 'moldavites' after the Moldau River, while 'bediasites' from Texas are named after the Bedias Indians. Others have acquired names from their places of occurrence ie. australites, javanites, and philippinites. 

The question of where and how tektites originated is still a matter of controversy, however most workers agree that they result from impact. Some argue that the impacts originally occurred on the moon, and that tektites represent ejected droplets of melted lunar rock which splashed onto the earth. However, none of the geological specimens collected from the moon during the Apollo missions could be regarded as the source of tektite glass. Many studies, though, relate them chemically and otherwise, to terrestrial materials. 

Bibliography

Arem, J.E. 1987. Color Encyclopedia of Gemstones. 2nd edition. Van Nostrand, New York. p.l86. 

Barnes, V.E and Barnes, M.A. 1973. Tektites. Dowden, Hutchinson and Ross Inc., Stroudsburg, Pennsylvania, USA. 

Koeberl, C. 1992. Geochemistry and origin of Muong Nong-type tektites. Geochimica et Cosmochimica Acta 56, 1033-1064. 

O'Keefe, J.A. 1976. Tektites and their Origin. Elsevier, Amsterdam-OxfordNew York.