by The Great Sand Sea Desert stretches over an area of 72,000 square kilometers connecting Egypt and Libya. If you find yourself in a particular part of the desert in southeast Libya and southwest Egypt, you will see pieces of yellow glass scattered across the sandy landscape.
It was first described in a scientific paper in 1933 and is called Libyan desert glass. It is prized by mineral collectors for its beauty, relative rarity and mystery. There is a piece of glass in a suit found in the tomb of the Egyptian pharaoh Tutankhamun. Natural glasses are found elsewhere in the world; Examples include moldavites from the Ries crater in Europe and tektites from the Ivory Coast. But none is so rich in silica as the glass of the Libyan desert, and they are not found in such large lumps and quantities.
The origin of glass has been a matter of debate among scientists for almost a century. Some suggested it could be from volcanoes on the moon. Others suggest that it is the result of lightning strikes (“fulgurites” – glass that forms from the fusion of sand and soil when struck by lightning). caused by a huge meteor explosion in the air; or that it came from a nearby meteorite crater.
Now, thanks to advanced microscopy technology, we believe we have the answer. Together with colleagues from universities and scientific centers in Germany, Egypt and Morocco, I identified the glass of the Libyan desert that came from the impact of a meteorite on the Earth’s surface.
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Under the microscope
In 1996 scientists determined that the glass was close to 29 million years old. A later study suggested that the original material consisted of quartz grains, coated with mixed clay minerals and oxides of iron and titanium.
This latter result raised more questions, since the proposed age is older than the matching source material in the relevant area of the Great Sand Sea desert. To put it simply: those original materials did not exist in that location 29 million years ago.
For our recent study, a co-author obtained two pieces of glass from a local who collected them in the Al Jaouf region of southeastern Libya.
We studied the samples with a state-of-the-art transmission electron microscopy (TEM) technique, which allows us to see tiny particles of material, 20,000 times smaller than the thickness of a sheet of paper. Using this super high magnification technique, we found small minerals in this glass: different types of zirconium oxide (ZrO2).
Minerals are composed of chemical elements, the atoms of which form a regular three-dimensional package. Imagine placing eggs or soda bottles on the supermarket shelf: layers upon layers to ensure the most efficient storage. Likewise, atoms assemble into a crystal lattice that is unique to each mineral. Minerals with the same chemical composition but different atomic structure (different ways of packing atoms into the crystal lattice) are called polymorphs.
One polymorph of ZrO2 we observed in Libyan desert glass is called cubic zirconia – the type seen in some jewelry as a synthetic replacement for diamond. This mineral can only form at a high temperature between 2,250 degrees Celsius and 2,700 degrees Celsius.
Another polymorph of ZrO2 we observed was a very rare one called ortho-II or OII. It creates at a very high pressure – about 130,000 atmospheres, a pressure unit.
Such pressure and temperature conditions gave us proof of the meteorite impact origin of the glass. That is because such conditions can only be found in the Earth’s crust through the impact of a meteorite or an atomic bomb explosion.
More mysteries to solve
If our findings are correct (and we believe they are), the parent crater – where the meteorite hits the Earth’s surface – should be somewhere nearby. The nearest meteorite craters, named GP and Oasis, are 2 kilometers and 18 kilometers in diameter respectively, and far away from where the glass we tested was found. They are too long and too small to be considered the parent craters for massive amounts of impact glass, all concentrated in one spot.
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So, while we’ve solved part of the mystery, there are still more questions. Where is the crater of the parents? How big is it – and where is it? Could it be corroded, deformed or covered in sand? Further investigations will be required, probably in the form of remote sensing studies combined with geophysics.
This article was originally republished on The Conversation.
