Friday, July 15, 2011

TEKTITES - from out of this world ?

Tektites (from Greek tektos, molten) are natural glass rocks up to a few centimeters in size, which most scientists argue were formed by the impact of large meteorites on the Earth's surface. Tektites are typically black or olive-green, and their shape varies from rounded to irregular. Tektites are still poorly understood. They are irregularly- and at times intricately-shaped nodules and blobs of a glassy substance. They have no crystal structure, and are therefore similar to Obsidian, but are not associated with volcanic processes.

This impact theory of Tektites relies on the observation that Tektites cannot be found in most places on the Earth's surface. They are only found in four strewnfields, three of which are associated with known impact craters. Only the largest and geologically youngest Tektite deposit in Southeast Asia, has not been definitively linked to an impact site, probably because even very large impact structures are often not easy to detect. Also, the bigger the strewnfield, the bigger the area to search for the crater. Since several new craters are identified every year, this is not really regarded as a problem by proponents of the Tektite impact theory.
The age of Moldavites, also miss-spelled Maldavite, a type of Tektite found in the Czech Republic, has been determined to be 14 million years. This age also exist for Tektites from the North American strewnfield and the Chesapeake Bay impact crater and Tektites from the Ivory Coast strewnfield and the Lake Bosumtwi-Crater.

Tektites are among the "driest" rocks, with an average water content of 0.005%. This is very unusual, as most if not all of the craters where Tektites may have formed were underwater before impact. Also, partially melted Zircons have been discovered inside a handful of tektites. This, along with the water content, suggests that the tektites were formed under phenomenal temperature and pressure not normally found on the surface of the Earth.

The various known Tektites are:

European strewnfield:
--Moldavites (Czech Republic, green)

Only Tektites from this area are clear or large enough to be faceted.
Australasian strewnfield:
--Australites (Australia, dark, mostly black)

--Indochinites (South East Asia, dark, mostly black)

--Chinites (China, black)

North American strewnfield:
--Bediasites (USA, Texas, reddish-black)

--Georgiaites (USA, Georgia, brownish-green)

Ivory Coast strewnfield:

--Ivorites (Ivory Coast, black)

Though the meteorite impact theory of Tektite formation is widely accepted, minority theories propose alternate ideas of Tektite formation.

Also do not confuse Tektites with Meteorities, which will be discussed in a later Blog.

Pictures of Tektites from those owned or from friends collections.