Study Sheds New Light on Origin of Libyan Desert Glass

Libyan desert glass is a natural glass found in western Egypt that formed 29 million years ago, however its origin is disputed: the two main formation hypotheses include melting by meteorite impact or melting by a large atmospheric airburst. A new study by a duo of researchers from Australia and Austria supports the hypothesis that Libyan desert glass was created by a meteorite impact.

Nearly pure silica, the canary yellow Libyan desert glass was famously used to make a scarab that is part of Tutankhamun’s pectoral. Image credit: Jon Bodsworth.

Nearly pure silica, the canary yellow Libyan desert glass was famously used to make a scarab that is part of Tutankhamun’s pectoral. Image credit: Jon Bodsworth.

Curtin University’s Dr. Aaron Cavosie and his colleague, Professor Christian Koeberl from Austria’s Natural History Museum and the University of Vienna, examined tiny grains of the mineral zircon in samples of Libyan desert glass.

“Zircons in the glass preserved evidence of the former presence of a high-pressure mineral named reidite, which only forms during a meteorite impact,” Dr. Cavosie said.

“It has been a topic of ongoing debate as to whether the glass formed during meteorite impact, or during an airburst, which happens when so-called near-Earth objects explode and deposit energy in the Earth’s atmosphere.”

“Both meteorite impacts and airbursts can cause melting, however, only meteorite impacts create shock waves that form high-pressure minerals, so finding evidence of former reidite confirms it was created as the result of a meteorite impact.”

The idea that the glass may have formed during a large atmospheric airburst gained popularity after an airburst over Chelyabinsk in 2013, which caused extensive property damage and injury to humans but did not cause surface materials to melt.

“Previous models suggested that Libyan desert glass represented a large, 100-Mt class airburst, but our results show this is not the case,” Dr. Cavosie said.

“Meteorite impacts are catastrophic events, but they are not common. Airbursts happen more frequently, but we now know not to expect a Libyan desert glass-forming event in the near future, which is cause for some comfort.”

The findings were published in the journal Geology.

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Aaron J. Cavosie Christian Koeberl. Overestimation of threat from 100 Mt-class airbursts? High-pressure evidence from zircon in Libyan Desert Glass. Geology, published online May 2, 2019; doi: 10.1130/G45974.1

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