fulgurite - natural glass flanged tube formed by lightning strike on sand from the Western Sahara in Morocco

Fulgurites form when a lightning bolt strikes the earth’s surface, fusing the material into glass, sometimes with as a tube a hollow center, sometimes flanged, as with these. When lightning strikes sandy soil, the air and moisture in the sand are rapidly heated. Quartz sand melts at a temperature of roughly 1600˚C to 2000˚C depending on the moisture content. The name comes from the Latin fulgur, for lightning.

Nomads occasionally collect these from a western Sahara dune field in Morocco. We have not seen these previously.

These are Type 1 fulgurites, sand fulgurites, as classified by Matthew A. Pasek et al in Fulgurite morphology: a classification scheme and clues to formation, Contributions to Mineralogy and Petrology 164 (3): 477 - 492 [2012]. Type 1 fulgurites form in sand as tubular structures, sometimes with the central opening collapsed, and frequently coated with sand.

There is little lightning activity in the Sahara today, so the fulgurites found in the Sahara confirm that very different conditions existed in prehistoric times. Since fulgurites are glass, they are resistant to weathering and are usually well preserved for long periods of time.

Because fulgurites are amorphous, they are classified as a mineraloid.

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