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A tube fulgurite and a more irregular specimen.

Fulgurites (from the Latin fulgur, meaning "thunderbolt") are a variety of the mineraloid lechatelierite. Sometimes referred to as petrified lightning, they are natural hollow glass tubes formed by lightning strikes in quartzose sand, silica, or soil.[1]


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 grains together; the fulgurite tube is the cooled product.[2] This process occurs over a timespan of around one second,[3] and leaves evidence of the lightning path and its dispersion over the surface or into the earth, [4]

Fulgurites can also be produced when the cables of a high voltage electrical distribution network break, and the lines fall onto a conductive surface beneath in the presence of loose sand. The glass formed, called lechatelierite, may also be formed by meteorite impact and volcanic explosions. Because it is amorphous in structure, fulgurite is classified as a mineraloid.

Fulgurites can be up to several centimeters in diameter and can have deep penetrations, sometimes occurring as far as 15 metres (49 ft) below the surface that was struck.[5] 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.[3] The Yale University Peabody Museum of Natural History displays the longest known preserved fulgurite, approximately 13 feet (4.0 m) in length.[6] Charles Darwin in The Voyage of the Beagle recorded that these tubes found in Drigg, Cumberland, UK reached a length of 30 feet (9.1 m).[citation needed]

The 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. They are rootlike in appearance and often show branching or small holes. Fulgurites occasionally form as glazed tracks on solid rocks (sometimes referred to as an exogenic fulgurite).[7]


Fulgurites are appreciated by many for their scientific value as permanent tangible evidence of transient lightning strikes.[8] The fact that fulgurites are abundant in the Saharan Desert shows that lightning was once a frequent occurrence in that region.[9]

Fulgurites are also popular among hobbyists and collectors of natural specimens.[10]

Fulgurite is very fragile.


  1. ^ Codding, Penelope W. (1998). Structure-based drug design. Springer. p. 27. ISBN 0-7923-5202-5. 
  2. ^ Carl Ege. "What are fulgurites and where can they be found?". geology.utah.gov. Retrieved 2009-03-21. 
  3. ^ a b Grapes, R. H. (2006). Pyrometamorphism. Springer. p. 28. ISBN 3-540-29453-8. 
  4. ^ Uman, Martin A. (2008). The Art and Science of Lightning Protection. Cambridge University Press. p. 212. ISBN 0-521-87811-X. 
  5. ^ Ripley, George; Charles Anderson Dana (1859). The New American Cyclopaedia. Appleton. p. 2. 
  6. ^ "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. 
  7. ^ 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.)
  8. ^ Chambers's journal By William Chambers, Robert Chambers
  9. ^ Vladimir A. Rakov, Lightning Makes Glass, 29th Annual Conference of the Glass Art Society, 1999, University of Florida, Gainesville
  10. ^ Patti Polk, Collecting Rocks, Gems & Minerals: Easy Identification - Values - Lapidary Uses, Krause, 2010, page 168 ISBN 978-1-4402-0415-9

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