Note: No Trees Were Harmed in the Making of this Post


What on Earth was that? A branch? A piece of coral? The petrified arm of an Ent? No, as many of you guessed, it’s a fulgurite!

A what?

Fulgurites form in a flash – when lightning strikes simple beach sand or desert soil on a surface that conducts electricity, such as water, at a temperature of at least 3,270 degrees Fahrenheit (1,800 degrees Celsius). The extreme heat forces the grains of sand (or sometimes soil or rock) to melt and fuse together. The product cools, producing a hollowed glass structure that mimics the appearance of a tree root or large branch.

Photographer Stan Celestian found this 14-inch sand fulgurite on the outskirts of Queen Creek, Arizona on May 4, 2005. He submitted the image recently to the Earth Science Picture of the Day Web site , where it appeared on October 26th.

Why the odd shape, you might wonder? The lightning bolt fans out in several directions as it hits the water in an attempt to release its energy. The length of each “branch” of a fulgurite is equivalent to how quickly each path of the lightning strike exhausted itself of energy.

Fulgurites are rare enough to cost hundreds of dollars depending on size and shape, and intriguing enough to be the focus of research projects. A 2009 University of Arizona-Tucson study , for example, found that fulgurites contain a partially-oxidized form of phosphorus called phosphite that early microbes may have thrived on as a nutrient.

This summer, a NASA-funded study revealed that fulgurites can experience a range of temperatures during formation.

So, next time you want to impress your friends with arcane but fascinating trivia, ask if they know what a fulgurite is. When they scratch their heads and offer blank stares, boot up your laptop, show them our What On Earth #5 post and explain this fluke of nature. You’re sure to dazzle them with your extra-ordinary intelligence and one of the marvels of science.

Gretchen Cook-Anderson, NASA’s Earth Science News Team