Fulgurites (from the Latin fulgur meaning thunderbolt) are natural hollow glass tubes formed in quartzose sand, or silica, or soil by lightning strikes. They are formed when lightning with a temperature of at least 1800 °C (3270 °F) instantaneously melts silica on a conductive surface and fuses grains together; the fulgurite tube is the cooled product. This process occurs over a period of around one second, and leaves evidence of the lightning path and its dispersion over the surface. Fulgurites can also be produced when a high voltage electrical distribution network breaks and the lines fall onto a conductive surface with sand beneath.

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