Fulgurite — a world record

In December 2025, I was digging in my backyard with a shovel and ran into a fairly large, hard object. When I looked down to investigate, I saw what looked like an irregularly shaped rock made out of glass (silica dioxide, SiO2). Large rocks are not commonly found in the soil on Amelia Island, so I had to think for a minute. What is this? When I pulled the object from the ground, I immediately recognized that it might be a fulgurite! 

Fulgurites, often called fossilized lightning, are rock clumps formed when lightning instantaneously melts the ground during a strike, with electricity and heat flowing through the ground transforming whatever material it strikes.

Lightning rapidly vaporizes and melts the material in the ground, which on a barrier island is usually sand, which is primarily quartz (SiO2). Lightning heats the air inside of its plasma channel to roughly 40,000 degrees Celsius. This is up to five times hotter than the surface of the sun, and lasts only a fraction of a second. This discharge of energy into the ground results in the formation of branching, uniquely structured glassy tubes.

I moved to Florida 26 years ago and have heard of lightning hitting the beach and creating a fused glass structure, but I had never seen one in person. The one I found in my backyard was massive, a huge chunk of glass. I was so excited. With a degree in geology, I have a special place in my heart for all things rocks! 

I did a little research on the internet, but could not find an image of a fulgurite similar to the one I had found. I figured I either had a museum-quality specimen or a misidentification. I searched for an expert who could possibly verify my find. I have had many positive experiences reaching out to university researchers and professors to ask questions about interesting things I have found in the past. In my experience, they tend to respond fairly quickly to curious citizens, and this proved to be true again this time. 

I emailed the leading expert on fulgurites, Dr. Martin Uman, who spent his career with the University of Florida’s Camp Blanding International Center for Lightning Research and Testing and served as the chair of the Department of Electrical and Computer Engineering at UF from 1991-2003. He immediately responded to my email.

He looked at the images I sent him, and to my disappointment, he replied that my fulgurite was most likely man-made. He still referred to it as a fulgurite but explained that because it did not have the typical features associated with natural fulgurites, it was probably formed from a sustained discharge on the ground from a downed power line rather than lightning. Lightning causes fulgurites that are generally more intricate, hollow, and branching, not solid and massive.

I wanted Dr. Martin Uman to be wrong about my fulgurite, but arguing with a world-renowned fulgurite expert seemed pointless. Well, my specimen was still very cool!

In 1996, Dr. Martin Uman and his research team from UF achieved the record for the longest excavated fulgurite in the world, found at Camp Blanding’s U.S. Army National Guard located in Clay County, Florida. The prize fulgurite had two branches extending down from the strike point, one 5.2 m (17 feet) and the other 4.9 m (16 feet) long. This is still a world record!

With Florida being known as the lightning capital of the world, fulgurites form regularly across the state. While potentially thousands of strikes occur daily in the summer months, only about 1-5% of land strikes generate fulgurites. They are most commonly found in Central Florida's quartz-rich sand hills, in phosphorus mines, and less commonly on beaches and dunes.

Although it is rare to find one, it is not impossible!