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fulgurite

Fulgurites (from the Latin fulgur meaning thunderbolt) are natural hollow carrot-shaped glass tubes formed in quartzose sand or soil by lightning strikes. In the right kind of sand the extreme heat generated will form silica glass shapes that trace the path of the lightning. The structures are also known as Petrified Lightning.

The tubes can be up to a couple of centimeters in diameter, and meters long. Their colour 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. They are rootlike in appearance and often show branching or small holes. Fulgurites occasionally form as glazing on solid rocks.

Fulgurites are a very rare phenomenon. A very large one was found in South Amboy, New Jersey. This was roughly nine feet long with a diameter of three inches near the surface of the ground, and tapered to roughly three sixteenths of an inch in diameter at the deepest point recovered. As is often the case due to the fragile nature of fulgurites, scientists were unable to extract it in one piece and the largest recovered fragment was a mere six inches long.

Fulgurites are notably found high on Mount Thielsen ("the lightning rod of the Cascade Range") where they form a brownish-green glaze on rocks (especially on the final five or ten feet of the summit pinnacle) and on the shores of the Great Lakes.

Possibly the finest fulgurite sample on display can be seen in Philadelphia, USA, at the Academy of Natural Sciences. It was discovered in 1940.

Petrified lightning featured in the movie Sweet Home Alabama where the lead male character 'Jake' attempts to manufacture fulgurite by placing metal poles into the sandy beach during a thunderstorm to channel the lightning into the ground. Something similar happened in 2004 on Memorial Day in Huntsville Alabama when lightning struck a high tension power pole. The lightning bolt travelled through the metal guy-wire into the sandy soil at the base of the pole forming a green coloured glassy substance.

The largest fulgurite known is at the Peabody Museum of Natural History at Yale University, which has on display a 13-foot long fulgurite from the shores of Lake Congamond in northern Connecticut. The fulgurite has been on display at the Museum since the 1950s. It is viewable in the new Hall of Minerals, Earth and Space as of May, 2006.

• Picture of fulgurite found in Arizona
• Fulgurites created by lightning triggered by rockets, by American artist Allan McCollum
• Interview (THE EVENT: PETRIFIED LIGHTNING FROM CENTRAL FLORIDA) with Allan McCollum and associated mass quantities of PDF's related to the subject.
• Lightning Makes Glass lecture by professor Vladimir A. Rakov, PhD (University of Florida, Department of Electrical and Computer Engineering).
• Fulgurites as melted volcanic rock created by lightning hitting the summit of Shastina in northern California, by geologist Michael Diggles
• Glossary of Meteorology definitions (including Fulgurite).
• wvlightning.com definitions (including fulgurite).
• Petrified Lightning by Peter E. Viemeister (pdf)