Tektite

Tektites (from Ancient Greek τηκτός (tēktós) 'molten') are gravel-sized bodies composed of black, green, brown or grey natural glass formed from terrestrial debris ejected during meteorite impacts.

Finally, a few tektites contain partly melted inclusions of shocked and unshocked mineral grains, i.e. quartz, apatite, and zircon, as well as coesite.

Unlike terrestrial volcanic glass, a tektite produces only a few bubbles at most when heated to its melting point, because of its much lower water and other volatiles content.

They have a chunky, blocky appearance, exhibit a layered structure with abundant vesicles, and contain mineral inclusions, such as zircon, baddeleyite, chromite, rutile, corundum, cristobalite, and coesite.

[6][7] Most tektites have been found within four geographically extensive strewn fields: the Australasian, Central European, Ivory Coast, and North American.

A limited amount of evidence is interpreted as indicating that the proposed Central American strewn field likely covers Belize, Honduras, Guatemala, Nicaragua, and possibly parts of southern Mexico.

[19] The overwhelming consensus of Earth and planetary scientists is that tektites consist of terrestrial debris that was ejected during the formation of an impact crater.

In addition, some tektites contain relict mineral inclusions (quartz, zircon, rutile, chromite, and monazite) that are characteristic of terrestrial sediments and crustal and sedimentary source rocks.

Their geochemistry suggests that the source of Australasian tektites is a single sedimentary formation with a narrow range of stratigraphic ages close to 170 Mya, more or less.

Alternatively, various mechanisms involving the dispersal of shock-melted material by an expanding vapor plume, which is created by a hypervelocity impact, have been used to explain the formation of tektites.

As early as 1897, the Dutch geologist Rogier Diederik Marius Verbeek (1845–1926) suggested an extraterrestrial origin for tektites: he proposed that they fell to Earth from the Moon.

[25] From the 1950s to the 1990s, O'Keefe argued for the lunar origin of tektites based upon their chemical, i.e. rare-earth, isotopic, and bulk, composition and physical properties.

[5][25] Chapman used complex orbital computer models and extensive wind tunnel tests to argue that the so-called Australasian tektites originated from the Rosse ejecta ray of the large crater Tycho on the Moon's near side.

For example, one problem with the lunar origin theory is that the arguments for it that are based upon the behavior of glass melts use data from pressures and temperatures that are vastly uncharacteristic of and unrelated to the extreme conditions of hypervelocity impacts.

[29][30] In addition, various studies have shown that hypervelocity impacts are likely quite capable of producing low-volatile melts with extremely low water content.