Fulgurite: How Lightning Makes Glass Out of Sand

When you think of glass, you probably picture a cup that holds your tea or the windows in your living room. But did you know that lightning can create glass, too?

Lightning is one of nature’s spectacular shows of force–and it's power isn’t lost upon anyone who’s ever had a close encounter. Lightning can strike up to 10 miles from its point of origin, can be as hot as 54,000 degrees and can discharge between 100 million and 1 billion volts. Lightning can be frightening, but it can also be very beautiful.

And the intrinsic beauty of lightning can be captured indefinitely – by sand.

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Fulgurite, or petrified lightning as it’s sometimes called, is formed after lightning hits sand that’s high in silica or quartz. In fact, fulgurite gets its name from the Latin word “fulgur,” which translates to lightning in English.

As a bolt of lightning passes through sand, the intense heat – which is as hot or hotter than the surface of the sun – fuses the sand particles together to form a tube of glass.

A Powerful Lightning Strike

A lightning strike in Albuquerque, N.M. (iWitnessWeather/Nu66ie)

LARGER IMAGE

Perhaps you’ve been walking on a beach and came across an irregular and out-of-place rock, like the one to the right. That may have been fulgurite.

A typical fulgurite will look like an elongated, congealed mass of sand grains. It will also be hollow and the inside will be as smooth as professionally blown glass. The color of a fulgurite is directly tied to the type of sand in which it was formed.

Fulgurite can be found all over the world, from the beaches of the Gulf of Mexico to the Australian coast and even in the middle of Africa’s Sahara Desert.

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Fulgurite can be buried beneath the sand for weeks, months or even decades. Stumbling upon a fulgurite is rare, especially considering the delicateness of the glass and the destructive nature of the elements.

That’s why fulgurites, especially larger specimens, can cost hundreds of dollars.

So the next time you’re seashell hunting on the beach, be on the lookout for any odd-looking rock. It very well might be a fulgurite.