|A tube fulgurite and a more irregular specimen.|
Fulgurites (from the Latin fulgur, meaning "thunderbolt") are a variety of the mineraloid lechatelierite. They are natural hollow glass tubes often formed during lightning strikes, in quartzose sand, silica, or soil. Sometimes they are referred to as petrified lightning. Fulgurites may be instances of Lichtenberg figures, which are branching patterns formed by high-voltage discharges such as lightning.
Fulgurites are formed when lightning with a temperature of at least 1,800 °C (3,270 °F) instantaneously melts silica on a conductive surface and fuses mineral grains together; the fulgurite tube is the cooled product. This process occurs over a timespan of around one second, and leaves evidence of the lightning path and its dispersion over the surface or into the earth. Fulgurites can also be produced when the cables of a high voltage electrical distribution network break, and the wires fall onto a conductive surface beneath, in the presence of loose sand.
The glassy substance, called lechatelierite, also may be formed by meteorite impacts and volcanic explosions, but the products of such events do not take the characteristic shape of fulgurites. Because it is amorphous in structure, fulgurite is classified as a mineraloid.
Fulgurites may be up to several centimeters in diameter and can penetrate deep into the soil, sometimes occurring as far as 15 m (49 ft) below the surface that was struck. One of the longest fulgurites to have been found in modern times was a little over 4.9 m (16 ft) in length, and was found in northern Florida, US. The Yale University Peabody Museum of Natural History displays the longest known preserved fulgurite, approximately 4 m (13 ft) in length. Charles Darwin in The Voyage of the Beagle recorded that tubes such as these found in Drigg, Cumberland, UK reached a length of 9.1 m (30 ft).
The color varies depending on the composition of the sand in which they formed, ranging from black or tan, to green or a translucent white. The interior normally is very smooth or lined with fine bubbles; the exterior generally is coated with rough sand particles and is porous. Fulgurites are rootlike in appearance and often show branching or small holes. Fulgurites formed in sand or loose soil are mechanically fragile, making the field collection of large specimens difficult.
Fulgurites occasionally form as glazed tracks on solid rocks (sometimes referred to as an exogenic fulgurite).
Fulgurites are appreciated by many for their scientific value as permanent tangible evidence of transient lightning strikes. For instance, the fact that fulgurites are abundant in the Saharan Desert demonstrates that lightning once was a frequent occurrence in that region.
Fulgurites also are popular among hobbyists and collectors of natural specimens.
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- Carl Ege. "What are fulgurites and where can they be found?". geology.utah.gov. Retrieved 2009-03-21.
- Grapes, R. H. (2006). Pyrometamorphism. Springer. p. 28. ISBN 3-540-29453-8.
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- Ripley, George; Charles Anderson Dana (1859). The New American Cyclopaedia. Appleton. p. 2.
- "New Peabody hall offering high-tech lessons about Earth and space". Yale Bulletin & Calendar (Yale University) 34 (30). June 9, 2006. Retrieved 2013-12-26.
- Exogenic fulgurites from Elko County, Nevada: a new class of fulgurite associated with large soil-gravel fulgurite tubes (Rocks & Minerals, Sep/Oct 2004, Vol. 79, No. 5.)
- Chambers's journal By William Chambers, Robert Chambers
- Vladimir A. Rakov, Lightning Makes Glass, 29th Annual Conference of the Glass Art Society, 1999, University of Florida, Gainesville
- Patti Polk, Collecting Rocks, Gems & Minerals: Easy Identification - Values - Lapidary Uses, Krause, 2010, page 168 ISBN 978-1-4402-0415-9
|Wikimedia Commons has media related to Fulgurites.|
- Fulgurites in New Scientist (subscription required)
- Glossary of Meteorology definitions (including Fulgurite).
- Petrified Lightning by Peter E. Viemeister (pdf)
- Mindat with location data
- W. M. Myers and Albert B. Peck, A Fulgurite from South Amboy, New Jersey, American Mineralogist, Volume 10, pages 152-155, 1925
- Vladimir A. Rakov, Lightning Makes Glass, 29th Annual Conference of the Glass Art Society, Tampa, Florida, 1999
- Interview (The Event: Petrified Lightning from Central Florida) with artist Allan McCollum along with an historical archive of sixty-six downloadable PDF's on the subject of fulgurites.
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