THE GEMSTONE LIBRARY
Libyan Desert Glass
Natural silica-rich desert glass and the impact evidence preserved within it.
Natural glass from the Great Sand Sea
Libyan Desert Glass is a natural silica-rich glass associated with the Great Sand Sea in western Egypt, near the Libyan border. Its familiar name refers to the wider desert region; it should not be read as a promise that a specimen was collected within modern Libya. Published research dates the glass to approximately 28.5–29 million years ago.
Glass lacks the long-range repeating atomic arrangement of a crystal. This is why a translucent piece can resemble a pale yellow crystal while belonging to a different material category. The March photograph shows irregular, pale yellow translucent pieces from our collection. Their surfaces and shapes make them especially interesting as objects to examine in changing light.
The reidite fingerprint
The strongest part of the 2019 zircon study is its pressure evidence. Zircon and reidite have the same chemical formula, ZrSiO₄, but their atoms occupy different crystal arrangements. Reidite is the denser high-pressure form. The study describes pressures of about 30 gigapascals, far beyond the atmospheric overpressure associated with an airburst.
The researchers did not simply find intact reidite crystals in every glass fragment. They examined tiny newly formed zircon grains whose systematic orientation relationships record transformation back from reidite. This surviving crystallographic pattern is evidence of the mineral’s former presence, even after subsequent heating and transformation.
The authors concluded that this record requires high-pressure shock waves and excludes formation by an airburst alone. It is the combination of heat and pressure evidence that makes the interpretation persuasive: heat can accompany both proposed mechanisms, whereas the zircon fingerprint records the extreme shock conditions.
Reading the evidence at different scales
Our June photograph shows yellow translucency and the shapes of collection pieces. The impact argument operates at a much smaller scale, using mineral structures and microscopic shock features. A hand specimen lets us appreciate the material; crystallographic analysis reconstructs its formation history. Keeping those scales distinct makes the scientific story clearer.
Primary research
- Cavosie & Koeberl (2019), Geology 47: 609–612 · High-pressure evidence from zircon in Libyan Desert Glass
- Cavosie & Koeberl · Evidence of Former Reidite in Granular Zircon from Libyan Desert Glass, conference abstract
Evidence for an impact origin
The material’s formation was debated for decades, including whether the heat came from an impact at the ground or an atmospheric airburst. Research by Cavosie and Koeberl examined zircon grains in the glass and found evidence of the former presence of reidite, a high-pressure form of zircon. Curtin University’s explanation of their 2019 study emphasizes that the pressure required for this mineral points to a meteorite impact.
Separate research by Koeberl and colleagues reported shock features in quartz from bedrock in the glass region, also supporting a physical impact. These are microscopic geological observations, not something that can be confirmed from the yellow color of a hand specimen. The exact source crater remains a subject of investigation.
A terrestrial material with an extraordinary history
Libyan Desert Glass is best understood as Earth material transformed during an impact event. Calling it impact glass does not mean that every yellow fragment is a piece of the incoming meteorite. Scientific studies examine evidence within particular samples to reconstruct the event. Our photograph illustrates the collection material; it is not a laboratory identification of the photographed pieces.
Looking after irregular pieces
Keep pieces cushioned during storage, especially where narrow tips and thin edges might touch another object. Clean gently with a damp soft cloth, and avoid abrasive compounds, sudden temperature changes or impacts. Inspect an irregular edge before handling it closely. Preserving the surface allows both the translucency and the natural form to remain part of its appeal.
View this photograph in March 2025 Memory Lane →
Sources and further reading
- Curtin University · Impact evidence in zircon
- Koeberl et al. (2019) · Shocked quartz in the glass region
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