Tektites are glassy objects that are thought by most scientists today to be melt products of terrestrial rocks formed by hypervelocity impacts of large, extraterrestrial objects. They superficially resemble obsidian in appearance and chemical composition; however, several things distinguish these objects from obsidian. Primarily, they have a very low water content, a low alkali content, and they always contain lechatelierite (pure silica glass).They also often contain coesite (a highly dense silica polymorph), nickel-iron spherules, and baddeleyite (a zircon oxide mineral produced at very high temperatures during shock metamorphism), which lend evidence to a meteorite impact origin. Relict mineral inclusions often yield information about the tektite parent material.
Tektites are assigned to strewnfields, which are the areas over which chemically and physically related tektites are found. The assignment of a strewnfield is based on the oxide composition of a tektite. Four of the major strewnfields are the Australasian, Ivory Coast, Czechoslovakian, and North American strewnfields. Strewnfields include tektites, which are found on land, and microtektites, which are microscopic tektites that have been found in deep-sea sediments. Sizes range from less than 1 mm for microtektites to chunks 10-20 cm in width, with most being a centimeter or so in size and weighing a few grams (Glass, 1982). Tektites display a wide array of sizes, shapes, and surface features. For example, there are splash forms that include spheres, teardrops, dumbbells, and discs, ablated forms also known as "buttons", and chunks known as Muong Nong types that display a layered structure and are found primarily in Southeast Asia.
