Fulgurite

Fulgurite

Fulgurites [fuhl-gyuh-rahyts] (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 3,270 °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 lines break and fall onto a conductive surface with sand beneath. The glass formed is called lechatelierite which may also be formed by meteorite impact and volcanic explosions.

The tubes can be up to several centimeters in diameter, and meters long. Their color varies depending on the composition of the sand they formed in, ranging from black or tan to green or a translucent white. The interior is normally very smooth or lined with fine bubbles; the exterior is generally coated with rough sand particles and is porous.

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