Aterian flake tools and a unique material

Unable to post a long message due to server errors. Trying to create a thread with this short message to see if I can then add to it.
ROGER

Apparently not! Please don't add to this thread while I am trying to find a solution.

ROGER

Maybe it's too long... so let's try it in parts.

PART 1

So, let’s get this show on the road.

When Howard Carter discovered the tomb of Tutankhamun (1333-1323 BC) in the Valley of the Kings at Luxor, Egypt in 1922, amongst the fabulous jewels buried with the Pharaoh was a large gold pectoral (breastplate). A shimmering greenish-yellow stone carved in the shape of a scarab beetle was mounted as its centre-piece. This symbolized for ancient Egyptians the cosmic order to all living things, portraying the young sun-god Ra as a scarab with the wings, feet and tail of a falcon.



Carter had classified this gem as a piece chaldecony (a gem quality type of quartz), but in 1998 the Italian mineralogist Vincenzo de Michele was allowed access to it by the Museum of Cairo, checked it using a refractometer and confirmed it to be a piece of natural glass we now know as “Libyan Desert Glass” (“LDG” for short).

The stone is absolutely unique among ancient Egyptian jewellery and it is some indication of the esteem in which this material must have been held that it was used for such an important purpose. We now know that in Egyptian times, LDG would have been an infrequently-encountered material because it is found in only a single remote location

Discovery in 1932

In 1932, some ten years after Carter discovered the tomb, a desert survey expedition led by English geologist Patrick Clayton ventured southwest from Cairo to study the previously unexplored regions of the Sahara known as the “Great Erg” (also called the Egyptian Sand Sea). This area is actually a part of the Libyan Desert - north of a broad plateau called the Gilf Kebir. The primary goal of Clayton’s team was to try and locate the legendary oasis of Zerzura, a fabled desert city where contemporary accounts said that great riches were to be found.

Clayton didn’t find Zerzura, but members of his expedition discovered, scattered amongst the blackened rocks of the desert floor, transparent and translucent pieces of a pale yellowish vitreous substance that has since become known as Libyan Desert glass.

Despite the inaccessibility of the region and the harshness of the terrain, Clayton returned several times to collect samples of this glass, accumulating about 50Kg of it for study. On his last visit in 1934 he was accompanied by L. J. Spencer, then Keeper of Minerals at the British Museum. More recently there was a joint University of Texas/University of Libya expedition in 1971, when three scientists spent a fairly fruitless two hours searching the area and collecting just twenty-four samples. The area is, as you might expect, now “off-limits” to collectors and has been for some time.

There was another expedition in 1985 – the first of a series, as scientists began in earnest to try and unravel the mystery of how this glass had originated.

Distribution

The main area on the Egyptian-Libyan frontier where the glass is found is in the Egyptian part of the Libyan Desert. The strewn-field (the area in which the glass is distributed) is elliptical and roughly 80 by 30 miles. The glass is mainly concentrated in the sand-free corridors between a series of saifs (dunes) that rise abruptly to heights of over 300 feet above sharply contrasting weathered debris that overlies bedrock of Nubian Sandstone deposited during the Early Cretaceous Epoch some 100 million years ago.

...continues

PART 2

Characteristics

LDG represents the largest known deposit of a natural silica glass on Earth, the total mass of the deposit being estimated recently at some 1,500 Tons. The glass occurs in tiny flakes below a thousandth of an inch up to pieces the size of a bowling ball, weighing over 15 pounds. One spectacular piece weighed in almost 60 pounds. The glass has been reliably dated by fission-track methods at 29.5 million years old and is the purest natural silica glass ever discovered.

This purity gives the glass some remarkable properties. It can be heated up to 3,000 degrees Fahrenheit before it begins to melt (over 900 degrees higher than other natural glasses). It can be dropped into water when red hot and it will not shatter. (I’ve never tried this with my specimens and don’t intend to). High technology man-made glasses struggle to do better.

It is transparent to translucent in appearance, ranging from colourless, milky, smokey grey or pale peach through to more typical pale yellows and greenish-yellows - often with a gem-like quality. Unbroken pieces may exhibit triangular shapes with a fluted surface which are characteristics of “ventefacts” (rocks found in deserts where wind abrasion is common – now there’s another word for your vocabulary). They generally have an etched, frosted or pitted surface indicative of long periods of sand-blasting and scouring from the fierce Saharan winds. Frequently there are trails of small gas-filled vesicles (bubbles), wispy white deposits, and black swirls present. Geologically, there is nothing else quite like it.

Here is a reasonable sized specimen that shows these features nicely, photographed normally and with transmitted light:





The dark streaks within some samples of LDG are “rich” in iridium. Although the iridium level is only in the region of 0.5ppb, this is unusually high for terrestrial material. Most of Earth’s iridium migrated to its core with the majority of Earth’s iron and other heavy metallic elements. The iridium levels are consistent with levels found in meteorites and other cosmic debris that has arrived on Earth. The white deposit found as inclusions in many of the samples is cristobalite, a high-pressure polymorph of quartz which only forms at temperatures above 2,600 degrees Fahrenheit and is often found at sites of meteorite impacts.

The composition and structure of the glass are completely consistent with a hypothesis that it was formed from melted desert dune sand/sandstone arising from a meteorite or comet impact and that it subsequently cooled over a period greater than 24 hours in an Earth atmosphere.

Origins of LDG

To achieve such a high degree of purity the LDG pieces must be the form of natural impact glass (impactite) known generically as “tektites”, which are only formed at very high temperatures. The temperature at the impact site needs to reach at least 2,800 degrees Fahrenheit to generate such material.

LDG exhibits some distinct differences from most other tektite types. It has a uniformly higher silica content than other tektites, shows no evidence of aerodynamic sculpting and never occurs in the distinctive button, dumbbell, rod, sphere, disk or teardrop shapes characteristic of most other tektites. These shapes arise as a result of high velocity ‘splashing’ in a molten state, so the absence of such shapes suggests that LDG probably hasn’t travelled very far from the original impact site.

continues.....

PART 3

Impacts and Craters

The nearest large meteorite crater is some 90 miles to the west in Libya, but there is no evidence of impact glass at the site. In fact there are two other moderate sized craters in the vicinity of the glass - the largest being half a mile in diameter - but neither are large enough to explain the phenomenon. It would however be a remarkable coincidence to find such unusual material as LDG so close to relatively rare structures like astroblemes (deeply eroded impact features) without there being at least some relationship.

There has been no significant disruption to the surface rocks in the region, but this might be explained by the likelihood that the meteorite concerned exploded in mid-air above the desert (a so-called "soft impact"). This kind of event could certainly have been energetic enough to turn much of the desert sand and some of the bedrock into a vast lake of molten glass without necessarily moving it far from its original location, producing a large crater or leaving behind significant detectable quantities of extra-terrestrial debris.

Recent research by Mark Boslough of Sandia National Laboratories (working under contract to the US Department of Energy) concluded that the event which produced the glass was consistent with a 400 foot diameter asteroid entering the Earth’s atmosphere almost vertically at a speed of 12 miles per second, which broke up just before hitting the ground.

Such an impact would have generated a fireball that remained in contact with the Earth's surface at temperatures exceeding the melting temperature of quartz for more than 20 seconds – an effective yield of about 150 Megatons of TNT. Not only is this about 12,000 times the energy level the atomic bomb dropped on Hiroshima but, unlike a bomb-burst, the energy would all have been concentrated downwards. Momentarily, the temperature at the impact site would have been as hot as the surface of the Sun.

Afterwards, the molten glass may have flowed into low areas, puddled and cooled, gradually being broken up into smaller pieces by weathering. Certainly, rivers existed in this area in prehistoric times and these may also have assisted in breaking up and redistributing the glass.

Philippe Paillou of the Observatoire Aquitain des Sciences de L'Univers concluded that the Gilf Kebir was the largest impact crater field on Earth, based on the presence of numerous other smaller craters over the entire area. Collectively, these craters may well represent a series of multiple impacts all arising from a single meteorite shower.

In 2006, former NASA planetary scientist Farouk El-Baz, now a research Professor at Boston University, published what he claimed to be the definitive evidence for the impact theory – the discovery of the largest crater yet found in the Sahara.



The double-ringed structure is 20 miles in diameter across its outer rim, which is certainly large enough to be the source of the glass, if it is indeed a crater. Although located on the Gilf Kebir plateau, it is about 60 miles from the main concentration of glass. Given that there is no evidence of LDG travelling great distances through the atmosphere, we must speculate that either a vast shallow lake of molten material was formed which spread over this huge distance or that the LDG has subsequently been broken up and transported (perhaps by ancient rivers).

This as yet unconfirmed crater has been named "Kebira" (Arabic for "great" or "powerful"). While the extreme drought conditions of the Sahara generally act to preserve impact crater structures, El-Baz asserts that Kebira was difficult to see - partly because of its large size and partly because of its dissection and partial erosion by ancient rivers during a time when the region was considerably wetter than it is now.

continues...

PART 4

Paeolithic Tools

For the last 10,000 years the Great Erg has been an inhospitable place for human habitation. However, 50,000 years ago the area enjoyed a pleasant Mediterranean climate. In the late Palaeolithic era about 30,000 years ago and persisting until perhaps 18,000 years ago, the Aterian people were apparently the first to recognize the special properties of LDG. Like many types of glass, it flakes conchoidally - that is, by striking a glancing blow with another rock, or a baton of wood or bone, flakes may be removed in a predictable manner to produce a variety of efficient cutting edges.

The Aterian people used LDG to produce an array of skillfully-flaked bifaced points and other implements. After their expeditions in the 1930's, Clayton and Spencer reported that at least 10 percent of the LDG flakes recovered exhibited some sign of human workmanship. Virgil Barnes and James Underwood, who visited the LDG strewn field in 1971, reported that the largest specimen collected during their expedition - a tabular cobble weighing over 2 pounds – exhibited percussion marks suggesting that it may have been used as a pounding tool.

Although LDG produces sharp cutting edges and is harder than a steel penknife blade, it chips and breaks relatively easily compared to the rocks from which stone tools are usually made, so it is likely that the Aterian people selected LDG specifically for its aesthetic appearance or perhaps in the belief that it had some magical property.

continues...

PART 5 (final)

Flakes of LDG have also been found in localized concentrations suggesting the possible manufacture of implements in situ. Other fragments of the glass have been located over 400 miles from the known field.

Here’s a couple of flake tools, photographed normally and with transmitted light:






Many of the LDG fragments exhibit signs that they must have been exposed to the abrasive actions of wind and sand for a good deal longer than 30,000 years, before the Aterians worked them into tools. This makes it very odd that there is no evidence of man using LDG for the manufacture of lithic tools before Aterian times, even though Nubian Sandstone handaxes from much earlier cultures have been found in the same locality.

Barnes suggested that the area may have become covered by thick deposits of sand prior to the climatic perturbation of the late Pleistocene age which could have whipped the sand up into dunes, exposing the glass below. It is also possible that the glass lay on the surface for some 26 million years or so before the arrival of humans on the scene and was then covered for a short period up to about 30,000 years ago when the Aterian people discovered and began to utilize the material.

Roger (sorry I had to post several parts)

Very impressive read. I have seen a lot of Scarabs but never knew that tidbit of how they were mounted like this. Thanks for the post

buildsthefire wrote:

Slight correction on the interpretation of the scarab in the first post, it's actually Khepera, the Scarab god who rolled the sun across the sky (much the same way as scarabs roll animal dung). The distinction being that Khepera was the reason for the suns movements, while Ra was the embodiment of the sun itself.

Thanks, Owen. Quite right. Didn't intend to mislead anyone with my "poetic license".

Roger