Crystal Harvest Field Guide

Libyan Desert Glass: The Complete Guide

Pale yellow natural glass scattered across the dunes of western Egypt. It is almost pure silica, about 29 million years old, and was carved into a scarab for Tutankhamun. Here is what science now says about how it formed.

Quick facts

~98% SiO2One of the purest natural glasses known, mostly lechatelierite (natural fused silica).
~28.5–29 MaFission-track dating gives about 28.5 ± 0.8 million years.
Egypt, not LibyaFound in the Great Sand Sea of southwestern Egypt, near the Libyan border.
SG ~2.21RI about 1.46, both lower than ordinary window or bottle glass.
Hardness ~6About 6–6.5, softer than quartz.
>1,687 °CIts zircon grains broke down at temperatures above 1,687 °C, and perhaps near 2,750 °C.
Meteorite tracesDark layers are enriched in iridium, nickel, and cobalt in meteorite-like ratios.
King TutA carved scarab of desert glass sits at the center of a pectoral from Tutankhamun’s tomb.

From Stone Age tools to Tutankhamun to the lab

People have used this glass for thousands of years. Scientists have argued about its origin for nearly a century.

  1. PrehistoryStone Age people chipped the glass into tools, like obsidian. Microlithic tools at one camp date to about 10,000–7,000 years ago.
  2. c. 1323 BCA winged scarab of desert glass is set in a pectoral buried with Tutankhamun.
  3. 29 Dec 1932P. A. Clayton of the Survey of Egypt finds the glass field, with lumps up to 10 lb spread over at least 80 × 25 km.
  4. 1934Clayton and L. J. Spencer publish the first scientific description in Mineralogical Magazine.
  5. 1969–1990sFission-track dating establishes an age of about 28.5 million years.
  6. 1998Italian mineralogist Vincenzo de Michele identifies Tutankhamun’s scarab as Libyan Desert Glass.
  7. 2006Mark Boslough of Sandia National Laboratories proposes that a huge meteor airburst melted the sand.
  8. 2007El-Baz and Ghoneim propose the Kebira structure as a source crater. It remains unconfirmed.
  9. 2019Cavosie and Koeberl find evidence of reidite, a mineral that forms only at extreme shock pressures, in zircon grains in the glass. They conclude an airburst alone can’t explain it.
  10. 2023Kovaleva and colleagues find a high-pressure form of zirconia, adding to the impact evidence.

How it formed

The glass is melted local sand and sandstone. The question has always been what melted it.

  1. Pure quartz sand. The Nubia Formation sandstone and dune sands of the region are nearly pure quartz. That is why the glass is about 98% silica.
  2. A cosmic event. About 29 million years ago, a meteorite impact, or possibly a massive airburst, delivered enormous heat and pressure.
  3. Melting. Sand melted at temperatures above 1,687 °C, and possibly about 2,750 °C, near the boiling point of silica.
  4. Shock. Zircon grains record pressures above 30 GPa, which points to an actual impact rather than heat alone.
  5. Cooling. The melt cooled into glass, trapping swirls, bubbles, and traces of the impactor in dark layers.
  6. Wind and time. Millions of years of sand-blasting frosted and sculpted the surfaces we see today.

No confirmed crater has been found. The proposed Kebira structure is disputed, and shocked quartz in nearby bedrock hints at a deeply eroded impact site.

Where it’s found

The glass lies in corridors between huge dunes in the southwestern Great Sand Sea, north of the Gilf Kebir plateau.

Great Sand Sea

Southwestern Egypt

Estimates of the scattered field range from about 2,500 to 6,500 km², so “several thousand square kilometers” is safest.

Gilf Kebir National Park

Egypt, est. 2007

A 48,533 km² protected area that includes the silica glass area.

How much is left

Estimated 1981

At least about 1,400 tonnes remained on the surface, and the original amount may have been far larger.

What’s inside the glass

Lechatelierite

Natural fused silica, the bulk of the glass.

Cristobalite

Tiny crystals of a high-temperature silica mineral.

Schlieren

Swirling flow lines frozen in the glass.

Bubbles

Gas bubbles trapped as the melt cooled.

Dark streaks

Layers enriched in meteorite-derived iridium, nickel, and cobalt.

Zircon and baddeleyite

Zircon grains broken down by heat and shock, the key evidence for impact.

Real vs. fake desert glass

Yellow glass is easy to make, so fakes are common. The best tests are physical.

PropertyLibyan Desert GlassMan-made glass
Specific gravityAbout 2.21Soda-lime glass is typically about 2.5
Refractive indexAbout 1.46Typically about 1.5 or higher
SurfaceWind-frosted, pitted, sculptedOften glossy or tumbled smooth
InsideSwirls, bubbles, sometimes dark streaks and white cristobalite specksUniform, or with perfectly round bubbles
ColorMostly pale yellow to yellow-green. Clear and dark-streaked pieces also occur.Often too bright, too even, or too green

It is not a true tektite. Tektites like moldavite were thrown far from their craters, while Libyan Desert Glass is an impact glass found near where it formed. See how to tell a space rock.

Myths vs. facts

Myth: It fell from the sky.

Fact: It is melted Egyptian sand. Only traces in the dark layers come from the impactor.

Myth: It’s a tektite like moldavite.

Fact: It is classed as an impact glass, found near where it formed. Moldavite is a true tektite from Germany’s Ries crater.

Myth: It comes from Libya.

Fact: The field is in southwestern Egypt. “Libyan Desert” is the regional name for the eastern Sahara.

Myth: Its origin is a total mystery.

Fact: Shock evidence in zircon strongly supports a meteorite impact, although no crater has been confirmed.

Myth: Kebira is the proven crater.

Fact: The Kebira structure is proposed and disputed.

Myth: All real desert glass is yellow.

Fact: Clear and dark-streaked pieces also occur.

Buying ethically

The glass field lies inside Egypt’s Gilf Kebir National Park. Egypt’s environmental agency reports the glass has been “widely collected in recent years” and warns that collecting destroys archaeological context.

  • Egypt’s antiquities law (Law 117 of 1983) covers prehistoric artifacts, so worked tools of desert glass are antiquities. The legal status of raw glass isn’t clearly spelled out.
  • Buy from established dealers who can explain where a piece came from.
  • Never buy or sell knapped tools or flakes, which are archaeological artifacts.
  • Be wary of very cheap “desert glass,” since fakes are common.

This is general information, not legal advice.

Care and display

Storage

At about 6, it can be scratched by quartz and harder stones. Store it separately.

Cleaning

Mild soap and water are enough.

Handling

Like all glass, it can chip on sharp edges. Handle over a soft surface.

Libyan Desert Glass in the shop

Hand holding several pale yellow translucent Libyan desert glass fragments
Libyan Desert Glass — Natural Tektite Lot, 3 Pieces$78.72
Large Libyan desert glass piece, pale yellow and translucent, on white paper
Large Libyan Desert Glass$196.78
See all desert glass

Frequently asked questions

How old is Libyan Desert Glass?

About 28.5–29 million years, from fission-track dating.

Why is it so pure?

It formed from local quartz sand, which is almost pure silica.

Was it really in King Tut’s tomb?

Yes. The scarab at the center of one of Tutankhamun’s pectorals is carved from it.

Who discovered it?

P. A. Clayton of the Survey of Egypt found the field on 29 December 1932. Stone Age people had used it long before.

How hot did it get?

Above 1,687 °C, and possibly about 2,750 °C.

Is it a meteorite?

No. It is melted Earth sand, possibly created by a meteorite impact.

How do you know if Libyan Desert Glass is real?

Genuine Libyan Desert Glass is pale yellow to yellow-green, translucent, and almost pure silica. Look for wind-polished or sandblasted surfaces from the desert, scattered bubbles, wispy streaks, and sometimes dark swirls or cristobalite spots inside. Fakes are usually bottle glass or resin: too uniform in color, too clear, too green or orange, or with molded shapes. Buy from sellers who state the source and sell by weight.

Is Libyan Desert Glass rare?

Yes. It is found only in one area: the Great Sand Sea of western Egypt near the Libyan border (despite the name, it is in Egypt). The field covers roughly 6,500 square kilometers, the supply is finite, and Egypt restricts collecting and export, so most material on the market comes from older stock.

Why is Libyan Desert Glass so expensive?

Because it is a natural glass from a single, remote, protected source, formed by an extraordinary event about 29 million years ago, and supply cannot be increased. Clear, bright yellow pieces with good surfaces cost the most; it is still often more affordable per gram than moldavite.

Where is Libyan Desert Glass found?

In the southwestern corner of Egypt, scattered between dunes in the Great Sand Sea, near the Gilf Kebir plateau. It is not found in Libya.

How was Libyan Desert Glass formed?

By intense heat from a cosmic event about 29 million years ago that melted desert sand into glass. Scientists long debated a meteorite impact versus an airburst (a fireball exploding above the ground); mineral evidence found in the glass, including a high-pressure form of zircon called reidite, supports an impact origin. Either way, temperatures were far hotter than any volcanic eruption.

What are the uses of Libyan Desert Glass?

Mainly collecting and jewelry. Ancient Egyptians valued it too: the scarab in a pectoral ornament from Tutankhamun’s tomb is carved from it, and Stone Age people made tools from it. It is also used in crystal-healing practices, though there is no scientific evidence for those effects. See our Libyan Desert Glass.

Keep reading

Sources and further reading

Estimates of the field’s size and the exact formation temperature vary. This page gives ranges.

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