Boss Byproducts: Fulgurites Are Fossilized Lightning

So far in this series, we’ve talked about man-made byproducts — Fordite, which is built-up layers of cured car enamel, and Trinitite, which was created during the first nuclear bomb test.

A fulgurite pendant.
A lovely fulgurite pendant. Image via Etsy

But not all byproducts are man-made, and not all of them are basically untouchable. Some are created by Mother Nature, but are nonetheless dangerous. I’m talking about fulgurites, which can form whenever lightning discharges into the Earth.

It’s likely that even if you’ve seen a fulgurite, you likely had no idea what it was. So what are they, exactly? Basically, they are natural tubes of glass that are formed by a fusion of silica sand or rock during a lightning strike.

Much like Lichtenberg figures appear across wood, the resulting shape mimics the path of the lightning bolt as it discharged into the ground. And yes, people make jewelry out of fulgurites.

Lightning Striking Again

Lightning striking a tree. Poor tree.
Image via NOAA’s National Severe Storms Laboratory

Lightning is among the oldest observed phenomena on Earth. You probably know that lightning is just a giant spark of electricity in the atmosphere. It can occur between clouds, the air, or the ground and often hits tall things like skyscrapers and mountaintops.

Lightning is often visible during volcanic eruptions, intense forest fires, heavy snowstorms, surface nuclear detonations, and of course, thunderstorms.

In lightning’s infancy, air acts as an insulator between charges — the positive and negative charges between the cloud and the ground. Once the charges have sufficiently built up, the air’s insulating qualities break down and the electricity is rapidly discharged in the form of lightning.

When lightning strikes, the energy in the channel briefly heats up the air to about 50,000 °F, which is several times the surface of the Sun. This makes the air explode outward. As the shock wave’s pressure decreases, we hear thunder.

Of Sand and Rock and Other Stuff

Fulgurites, also known as fossilized lightning, don’t have a fixed composition: they are composed of whatever they’re composed of at the time of the lightning strike. Four main types of fulgurites are officially recognized: sand, soil, caliche (calcium-rich), and  rock fulgurites. Sand fulgurites can usually be found on beaches or in deserts where clean sand devoid of silt and clay dominates. And like those Lichtenberg figures, sand fulgurites tend to look like branches of tubes. They have rough surfaces comprised of partially-melted grains of sand.

An assortment of sand fulgurites.
Sand fulgurites, aka forbidden churros. Image via Wikimedia Commons

When sand fulgurites are formed, the sand rapidly cools and solidifies. Because of this, they tend to take on a glassy interior. As you might imagine, the size and shape of a fulgurite depends on several factors, including the strength of the strike and the depth of the sand being struck. On average, they are 2.5 to 5 cm in diameter, but have been found to exceed 20 cm.

Soil fulgurites can form in a wide variety of sediment compositions including clay-, silt-, and gravel-rich soils as well as leosses, which are wind-blown formations of accumulated dust. These also appear as tubaceous or branching formations, vesicular, irregular, or a combination thereof.

Calcium-rich sediment fulgurites have thick walls and variable shapes, although it’s common for multiple narrow channels to appear. These can run the gamut of morphological and structural variation for objects that can be classified as fulgurites.

Rock fulgurites are typically found on mountain peaks, which act as natural lightning rods. They appear as coatings or crusts of glass formed on rocks, either found as branching channels on the surface, or as lining in pre-existing fractures in the rock. They are most often found at the summit or within several feet of it.

Fact-Finding Fulgurites

Aside from jewelry and such, fulgurites’ appeal comes in wherever they’re found, as their presence can be used to estimate the number of lightning strikes in an area over time.

Then again there’s some stuff you may not necessarily want to use in jewelry making. Stuff that can be found in the dark, dank corners of the Earth. Stay tuned!

22 thoughts on “Boss Byproducts: Fulgurites Are Fossilized Lightning

  1. Most range from white to black. Once in a while youll find them with green, gold or blue hues. The intensity of the strike plays the largest role in the fulgurites color but various impurities can have some influence as well.

    1. OOPS. This was meant to be in reply to Anonymous’ “Someone gave me a piece of fulgurite but it is black. Not sure if that is a common color for it to form or if it was simply misidentified.”

  2. So now I’m thinking about finding a nice beach and sticking a big iron rod in there to see if I could draw lightning and make a fulgurite factory. A sharp tip dissipates charge, so that’s not the right thing. I wonder if you could set up some franklin’s bells and when you notice a big charge accumulating, supercharge it by dumping in a whole lot of electrons and end up triggering a lightning strike.
    This is a terrible hobby.

        1. Martin Uman did similar work in Florida I think.

          I might have a spool of wire go into a bucket of pure silica….a big model spaceship filled with explosives in front of a green screen…

    1. Isn’t there a movie about an artist that does this? Sweet Home Alabama I think it was.

      Oh wait, that wasn’t the point of the movie? Growing up my sisters watched that a few times. The fulgurites were the the best part of the movie.

      1. no the point was the bitchy snotty wife returns home to get divorce papers signed and turns back into a human being. One of the devices used was the husband got his crap together and started pulling flawless blown glass sculptures (that IRL cost thousands of dollars) out of the beach like seashells. Its not a terrible movie, but its still pure crap

  3. Makes one wonder what kinda welds and scars are on the tops of towers made of iron. Purdue campus used to have two towers on top of the EE building that dwindled in use till hams had the run of it. A landmark but every lightning hit glitched so many computers so they took them down years ago.

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