With summer in full swing and a balmy sea breeze white capping the gulf from the southwest, the sails were full as our catamaran raced over the waves and rushed toward the big deserted beach at Keewaydin. The foaming wake we left behind was captured by the whitecaps, but not before the Marco skyline was softened by our distance offshore and a salty mist rising from the upcoming beach
Our near-coastal island jaunts are always in search of adventure, but with any given day, the weather can be as different as the passengers on board. Almost everyone will enjoy a sailboat ride, and everyone becomes adventurous upon landing on a desolate sandy beach. The incredible seashells scattered along our beaches always make great souvenirs, but on this sun-splashed and windswept day, there was a new and previously unheard of request and a lesson for all islanders about our amazing and dynamic South Florida environment.
After the sails were down and the boat rode at anchor, everyone climbed down and began to explore. The family onboard was unique and after only a few minutes ashore, it was easy to understand why.
“There are always some great conch shells near the water’s edge,” I offered as we began to walk the beach.
“That’s okay.” Dad smiled as he answered, “We’re not looking for shells we’re looking for fulgurite.”
“Looking for what?” I asked.
“It’s called fulgurite,” Dad explained. “You see, the wife and I are geologists. On every vacation, we always take the kids and explore for different minerals. In South Florida, we really expect to find fulgurite. Fulgurite is a geological term for lightning melted earth.”
Dad must have noticed my clueless expression because he then began to explain an incredible phenomenon and solve a mystery that has eluded me for years. After exploring Marco’s adjacent islands for over three decades, I was always stumped for an answer when sailing guests would approach me on a beach holding little black rocks that sometimes appeared to be burned out cinders or lava rock. With almost every beach I visited, the little black rocks could always be found. Most everyone looking at the blackened and misshapen little stones would often remark, “This is lava, right?”
My reply was always, “No, there are no volcanoes here; it looks like lava but honestly, I don’t know what it is.” For many years, I did not know what the little black stones were, until I met the family of geologists and learned about fulgurite!
Fulgurite is also known as petrified lightning or solidified lightning bolts. As we all know in summer, our South Florida thunderstorms can be scary and ferocious. Florida is the lightning capital of the world and Tampa—which means sticks of fire in Seminole—is the lightning capital of Florida.
When lightning strikes the ground, it melts the earth. According to the International Center for Lightning Research and Testing, the peak temperature of a cloud to ground lightning bolt is 30,000 degrees Kelvin, or five times hotter than the surface of the sun.
Many will remember the film “Sweet Home Alabama,” where the story revolved around a principal character who placed lightning rods on a beach to attract lightning bolts that would melt the sand and make icicle-type glass curios to be sold in stores. In reality, many consider glass fulgurites to be an art form and valuable.
When lightning strikes silica sand, glass is produced. When lighting strikes our crushed shell beaches a different type of fulgurite is created. Our local beaches are made of nacre (a combination of calcium and protein) chitin, bone, cartilage and silica. When South Florida, cloud to ground lightning strikes our white sandy beaches, a type of fulgurite forms that resemble black popcorn in a very hard rock-like appearance. As a lightning bolt touches the sand with incredible temperature, the nacre melts instantly, and wherever moisture is present, steam forms and an explosion occurs. Our fulgurite is created in seconds and is shaped by moisture turning to steam. Holes are formed during the instant melting process when water turns to steam and pops.
After only a few minutes on the big Keewaydin Beach, the mom and dad geologists were examining some of the little black popcorn, cinder-type rocks that had been my personal mystery for years.
“This is the stuff,” they confirmed, “You have fulgurite everywhere!”
Fulgurite is indeed everywhere on our South Florida Beaches because unlike seashells, the little black lava-like stones do not break down into the sand. After being melted by a lightning strike five times hotter than the surface of the sun, the fused sand globules are permanent! They do not break down, and they are here to stay—older fulgurites may turn to a lighter tan color after aging in the sun.
Fulgurite can be easily found where seashells are abundant. Potential prospectors of solidified lightning need only have a little patience and a sharp eye. Any shape that resembles a blackened burned cinder or a lava rock is a geological example of the fiery force of Mother Nature.
After our exploration of the Keewaydin Beach was complete and a valuable new piece of information was logged aboard. Our catamaran set sail again for more adventures in the three decades of the Marco Beach Boy Chronicles.
Tom Williams is a Marco Islander. His debut adventure novel “Lost and Found” was ranked by Sport Diver Magazine in the top five books to: “Must take on vacation.” His second book “Surrounded by Thunder—the story of Darrell Loan and the Rocket Men,” was awarded the gold medal for non-fiction in the 2013 Florida Book Awards.