There’s a patch of the Sahara, right where Egypt runs into Libya, where you can pick chunks of pale yellow glass up off the sand. Not obsidian, not a dropped bottle. A natural glass, and the only place on Earth you’ll find it. It’s been sitting there for 29 million years, and it took scientists almost a century to agree on how it got there.
A find in the Great Sand Sea
The strewn field covers about 6,500 square kilometers of Egypt’s Great Sand Sea, hard against the Libyan border. English surveyor Patrick Clayton gets credit for the first scientific report, back in 1932, while he was out mapping dunes for the Egyptian Geological Survey. He wasn’t the first person to notice it, though. Archaeologists have found the glass knapped into Stone Age tools, so whoever was living in that stretch of desert tens of thousands of years ago had already worked out that it made a decent blade.
What actually made the glass
Dating puts the glass at around 29 million years old. Working out how it formed took a lot longer. It’s almost pure silica, something like 98%, well above any volcanic glass, and it contains lechatelierite, a form of fused silica that only shows up under extreme heat. That ruled out a volcanic origin fairly early. Left standing were two theories: a meteor exploding in an airburst overhead, hot enough to melt the sand below the way a nuclear test fuses a desert floor into glass, or an actual meteorite hitting the ground.
It wasn’t settled until 2024. Researchers ran samples through a transmission electron microscope and found grains of a rare zirconia form called orthorhombic-II zirconia, which only forms at pressures around 130,000 atmospheres. On Earth’s surface, as the research team pointed out, you get that kind of pressure from exactly two things: a meteorite impact or a nuclear detonation. Add in earlier evidence of reidite, a mineral found only at confirmed impact sites, breaking down into zircon under intense heat, and the case was closed. Something hit the ground here. Nobody’s found the actual crater yet. The known impact sites nearby are too small and too far off to account for a strewn field this size, so it’s either still buried under the dunes or eroded away completely.
A scarab in Tutankhamun’s tomb
Somebody in ancient Egypt was already onto this glass, long before anyone was arguing about airbursts and zirconia. When Howard Carter opened Tutankhamun’s tomb in 1922, one of the pieces he found was a pectoral built around a carved scarab, the beetle symbol of rebirth, made not from the usual turquoise or carnelian but from a piece of translucent yellow-green glass. Nobody knew what the material was for decades. Mineralogists didn’t match it to Libyan Desert Glass until 1998, which means someone, over 3,300 years ago, picked up a fragment of a 29-million-year-old impact site and carried it hundreds of miles to be carved for a pharaoh’s tomb.
Local Bedouin tradition calls it “the rock of God.” The strewn field has also turned up small diamond-bearing pebbles nearby, which has some researchers wondering whether the original impactor was a comet fragment rather than a stony meteorite, and it’s still legal to collect loose surface pieces in parts of the region today. Every piece sat in the sand for 29 million years before anyone picked it up. Ours has been sitting a lot less time than that.
