by Gerhard Müehle
February 1998

from Science Frontiers ONLINE Website
No. 64: Jul-Aug 1989

The Libyan Desert of Egypt is one of Earth's most remote and inhospitable regions.

Uninhabited, windblown and foreboding, the Sand Sea, near the Gilf Kebir Plateau, was nonetheless the site of a remarkable discovery in 1932.

The Egyptian Desert Surveys under the able direction of Englishman Patrick A. Clayton (1896-1962) recovered specimens (about 50 kg) of an unusual, often beautiful, translucent to transparent, yellowish-green gem-like, high silica natural glass.

After the 1932 discovery of Libyan Desert Glass, only two other expeditions (both of the 1930s) were undertaken to the location until 1971.

This latter exploration involved three scientists stopping over for only two hours and collecting some 24 samples of the glass. During this brief visit, the expedition accidentally found the site of a forced landing of an Egyptian aircraft with the remains of nine men.

The failure of Egyptian authorities to find the downed airplane for over three years is solemn validation of the remoteness of this arid region.

In light of the foregoing, it is perhaps remarkable that a greater abundance of Libyan Desert Glass has been made available recently for collections and study than at any time since its discovery 65 years ago.

Libyan Desert Glass is classified by most meteoriticists with the group of curious natural glasses known as tektites.

In 1900, Professor Franz E. Suess of Vienna coined the term tektite from the Greek tektos meaning "melted or molten." Tektites are compositionally restricted, high silica, natural glasses distinguishably different from other, volcanically derived, natural glasses.

Tektites range in size from microscopic (less than 1mm) to macroscopic weighing many kilograms. They exhibit a marvelous range of colors from water clear, gem quality, deep forest greens of moldavites to the soothing pale to dark yellow and yellow-greens of Libyan Desert Glass as well as the stygian, impenetrable black of Australites.

Isotopic data shows there are at least six recognized geographical distributions (strewnfields) of tektites on Earth. In addition, a few other concentrations of natural glasses are being studied for possible inclusion as bona fide tektites. The study of microtektites, in particular, has dramatically expanded the size of some of the known strewnfields.

Tektites are often confused with obsidian. While both are natural glasses, the volcanic origin of obsidians has been undeniably established.

The origin of tektites, on the other hand, is not well understood and the conflict of theories remains puzzling and unresolved.

In many ways, the large chunks of natural glasses such as Libyan Desert Glass and Muong Nong tektites are even more puzzling than the more traditionally recognized aerodynamic tektite forms.

Mankind has wondered about, and cherished, these enigmatic, exotic objects for hundreds of years, perhaps much longer. In the Cro-Magnon Venus of Willendorf site (Austria), dated at 29,000 BC, small moldavite flake blades were found (now lost!). The earliest written records come from mid-10th century China referring to the black, shiny objects found after rainstorms as lei-gong-mo, "inkstones of the thunder-god". Australian Aborigines called Australites ooga, "staring eyes".

The origin and source of tektites remains a mystery.

In a historical context, the earliest theories surmised an artificial provenance. (i.e. manmade glasses). Charles Darwin made the first scientific study of tektites (Australites) during his famous five year voyage on HMS Beagle. He deduced a volcanic origin. Fortunately his theory of evolution was more astute than his belief that tektites were volcanic bombs! His opinion on tektite origins, however, held sway until the beginning of the 20th century.

Since then, a multitude of other theories, including several extraterrestrial origin possibilities, have been advanced. Current opinions favor a terrestrial impact related paradigm. However, each proposed theory, while demonstrating evidence in its own favor, continues to frustratingly yield contradictory results favoring alternative origins.

In 1973, in Meteorites and Their Origin, the author notes,

"At present there is a conflict of evidence concerning the origin of tektites, a conflict that is only complicated by the introduction of refined instrumental methods of research. They appear sui generis, one of the unexplained natural science phenomena."

This statement is still valid almost a quarter of a century later.

In relation to all other tektite groups, Libyan Desert Glass exhibits a noteworthy number of unique attributes.

• Lowest refractive index: 1.4616

• Lowest specific gravity: 2.21

• Highest silica content: 98%

• Highest lechatelierite particles: fused quartz

• Highest water content: 0.064%

• Highest viscosity: almost 6X greater than Australites at the same temperature

• Other unique attributes: Color,

• Bubble types: 100% of included bubbles are lenticular or irregular.

Libyan Desert Glass is classified as a Muong Nong type of tektite, i.e. broken chunks from a layered mass. The three other classifications of tektites include,

1) the microtektites

2) splash form types (dumb-bells, drops, flattened spheres)

3) the most prized, flanged buttons

Hand specimens of Libyan Desert Glass, when help up to the light, readily reveal the internal layering and stratification of included bubbles and smoky, dusky-brown curtains of fine particulate matter.

There is no evidence whatsoever, of atmospheric aerodynamic shaping and it is therefore presumed that Libyan Desert Glass formed as a melt sheet of some sort, possibly by meteoritic impact some 28.5 millions years ago. Recent French studies concluded that meteoric elements in the glass, of almost chondritic proportions, "points to an impact origin".

Interestingly, the inclusion of the high number of lechatelierite (fused quartz) particles in Libyan Desert Glass also points to an extremely high, up to 1700° C, formation temperature. Impacts of large bodies at high velocity are certainly capable of creating such high temperatures. But, the central issue in determining the impact origin of tektites remains, that is, how to transform a mass of crushed rock into a homogeneous and relatively bubble free liquid which rapidly cools to a glass.

Even the commercial production of glass takes many hours to relieve the melt of its volatile components. No partially melted material, or target rock inclusions, have ever been found in Libyan Desert Glass. Furthermore, other known impact glasses (impactites) such as Darwin Glass are bubbly, frothy, scoriaceous and contain partially melted materials.

So the controversy continues.

Libyan Desert Glass is found widely scattered over an area 130 km north to south by 53 km east to west. Specimens are recovered in sand free corridors between 100 meter high, north-south trending sief dunes.

Wind driven desert sands now sculpt, shape and polish fragments of this rare, exotic glass into strikingly beautiful and unique specimens. Prized pieces exhibit pseudo-thumbprints, fluting pitting and smoothly polished surfaces.

Since 1994, thanks to the undaunting efforts of a few intrepid collectors, hundreds of fine specimens of Libyan Desert Glass have been made available for the collector and scientist. Unusual and rare types, with very dark-brown sometimes gray-blue streaked wispy interiors have been recovered. And others, laden with white spherical crystallites (cristobalite?), pique the interest of students and collectors alike. Manmade flake blade chips of great antiquity are also occasionally offered.

These hand-hewn objects astound us and are a link to our Neolithic ancestors of 10,000 - 20,000 years ago.
 

Samples