Fulgurite is a hollow, glassy tube formed when lightning strikes the ground. The tube has a rough exterior and either a rough or smooth interior. Fulgurites may be branched like a tree or Lichtenberg figure. They come in a range of colors, including white, brown, green, and black. Most fulgurites are impure silica glass (SiO2) and are classified as the mineraloid lechatelierite. Other forms of lechatelierite include tektites and trinitite.
The word fulgurite comes from the Latin word fulgur, which means thunderbolt. Sometimes fulgurites are called “petrified lightning.”
Types of Fulgurites
Scientists classify fulgurites based on the composition of the ground that forms them.
- Type I: Type I fulgurites form from cloud-to-ground lightning strikes on sand. This type of fulgurite takes the shape of a tube that may or may not have a collapsed center.
- Type II: Type II fulgurites form when lightning strikes soil. They may be hollow tubes, branching tubes, or irregularly-shaped and may have droplets or granules on their surface, depending whether the soil was rich in silt, gravel, dust, or clay.
- Type III: Type III fulgurites form in caliche or calcic sediment. This type of fulgurite has thick, sometimes glazed walls.
- Type IV: Lightning striking rock forms type IV fulgurites. These fulgurites look like a crust on the rock or a tunnel into it.
- Type V: Type V fulgurites are droplet fulgurites. The droplets may be round or filamentous. This type of fulgurite depends on shape and not soil composition.
Where to Find Fulgurites
Fulgurites form where lightning strikes, so it’s easiest to find them on mountain peaks, desert highlands, and beaches. Peaks known for fulgurites include the French Alps, Sierra Nevada range, Rocky Mountains, Pyrenees range, Cascades, and Wasatch range. Fulgurites often form along the Florida coastline, due to high lightning activity. But, they also occur around lakes and near other bodies of water. The Libyan desert contains fulgurites formed from pure white sand. Some clear fused quartz also occurs in this desert, but it may have formed from a meteor impact rather than lightning because of the extraordinary temperatures required to make it.
Fulgurites are available in stores and online. Reputable sellers tend to be geologists or rock hounds. Ideally, a listing includes the location of the find and its composition.
Three Ways to Make Fulgurites
If looking for fulgurites or buying them doesn’t interest you, consider making one yourself. Here are three methods:
Easy Way to Make a Fulgurite
It’s easy to make fulgurites by drawing lightning into sand or soil. However, you need to live somewhere that gets lightning for this method.
- Select the best area for the project. Choose an open area, away from people, animals, trees, or buildings. Ideally, it should be higher than its surroundings. Drive a lightning rod or length of rebar into sand so it extends at least one foot or half a meter into the air. It’s fine to use colored sand or another mineral besides sand (which is mostly quartz).
- Check the weather. Use radar and maps that record lightning strikes so you’ll be ready.
- Go far away from your project before and after the thunderstorm. Don’t venture outside until lightning is at least 5 miles from your location. Have your phone get weather alerts or use an app to track lightning so you’ll be safe.
- Allow time for the lightning rod and fulgurite to cool. Gently dig around the fulgurite to expose it before removing it. Fulgurites are delicate and easily damaged. Rinse off excess sand with water.
Make a Rocket Fulgurite
Rather than waiting for lightning to strike, draw the lightning using a D model rocket. Attach the rocket to a spool of copper wire and the end of the wire to a bucket of sand. Launch the rocket at a thunderhead. Anecdotally, this “Ben Franklin” method is highly successful. But, it’s not recommended because launching a rocket during a thunderstorm isn’t safe!
Make an Artificial Fulgurite
If you don’t get lightning where you live (or just want an interesting science project), use a transformer (e.g., XMFR) to force electricity into clean sand or pure silica. This makes an artificial fulgurite because it doesn’t rely on natural lightning. Because lightning strikes are more powerful than generated electricity, artificial fulgurites usually aren’t as branched as natural fulgurites.
People collect fulgurites for their interesting structures, but they have scientific uses, too. The number of fulgurites in an area indicates the frequency of lightning strikes over time. This helps scientists understand climate and how it has changed. Also, fulgurites are a natural source of some unusual minerals and chemical compounds. Some contain shocked quartz, which has a crystal structure different from regular quartz. They contain C60 and C70 fullerenes, silicon-metal alloys, and rare reduced phosphides [Fe3P, (Fe,Ni)3P, and Ti3P2].
- Daly, TK; Buseck, PR; Williams, P; Lewis, CF (2015). “Fullerenes from a fulgurite”. Science. 259 (5101): 1599–601. doi:10.1126/science.259.5101.1599
- Gailliot, Mary Patricia (1980-01-01). “Petrified Lightning”. Rocks & Minerals. 55 (1): 13–17. doi:10.1080/00357529.1980.11764615
- Pasek, Matthew A.; Block, Kristin; Pasek, Virginia (2012). “Fulgurite morphology: a classification scheme and clues to formation”. Contributions to Mineralogy and Petrology. 164 (3): 477–492. doi:10.1007/s00410-012-0753-5