Fulgurite
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Image:Fulgurite1.jpg Fulgurites (from the Latin fulgur meaning thunderbolt) are natural hollow carrot-shaped glass tubes formed in quartzose sand or soil by lightning strikes. When lightning hits the ground, electrons flow outwards in all directions, sometimes heating the ground to around 1800 degrees. In the right kinds of sand this will form silica glass shapes that trace the path of the lightning through the sand. For this reason the structures are also known as Petrified Lightning. They are up to a couple of centimeters in diameter, and can be meters long if they are carefully excavated so as not to break the fragile structure. 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, as well.
Naturally forming fulgurite is a very rare phenomenon. The largest ever found was in South Amboy, New Jersey. This was roughly nine feet long with a diameter of three inches near the surface of the ground which 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 fulgurite 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).
Arguably the finest fulgurite sample on display can be seen in Philadelphia 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 to this 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 Peabody Museum of Natural History, Yale University, has on display a fulgurite from the shores of Lake Congamond in northern Connecticut. It is 13 ft long, making it longer than the one in Philadelphia. The fulgurite has been on display at the Museum since the 1950's. It will be viewable in the new Hall of Minerals, Earth and Space after May, 2006. Related information on this fulgurite specimen available via the Division of Mineralogy, Yale Peabody Museum.