Imagine you’re journeying through the Sahara, the largest desert in the world, where temperatures can exceed 50°C (122°F) and sand dunes can be as high as 180 meters (590 feet). It’s the hottest part of the day and the Sun’s beaming down on you like a million flaming arrows. Sand, picked up by the fluctuating breeze, keeps getting thrown in your face, making your eyes sting. You’re uncomfortable, exhausted, and dehydrated. To make matters worse, the camel you’re riding looks about ready to collapse, so sluggish have his movements become. Suddenly, as predicted, you’re faithful four-legged friend topples over with a long, agonizing groan. One moment you find yourself slipping off his back; the next thing you know you’re rolling down the bank of the sand dune you were climbing. You land at the bottom stunned but unhurt.
After wiping the sand from your eyes, you notice at your feet a strange, dark object protruding a couple of inches above the sand. Reminiscent of a tree root, the object has a rough and bumpy exterior. Excited, you begin to dig away the sand around it. This is no easy task, as the object’s buried deep; it’s also very fragile. You discover to your amazement that the object is actually hollow, its central cavity lined with what looks like glass.
The object in question is known as a fulgurite (from fulgur, meaning “thunderbolt” in Latin). Fulgurites are nature’s way of preserving, in glassy form, bolts of cloud-to-ground lightning. Sometimes referred to as “petrified lightning,” the earliest recorded discovery of a fulgurite was in 1706 by a Pastor David Hermann in Germany. Fulgurites are formed when a lightning bolt of at least 18,000°C (32,432°F) strikes sand or some other kind of silica-rich soil, causing the grains to instantly melt and fuse together. This cools and hardens. What remains is a hollow glass tube—an extremely accurate record of the path the lightning took when it hit the ground.
Fulgurites are classified as mineraloids. They can be many different colors, including white, gray, black, or green; it depends on the type of sand in which they were formed. Some of the finest specimens come from white, clean sand with a high silica content. (Silica sand (or quartz sand) is the main ingredient used to make glass.)
Since the diameter of a lightning channel varies from one to two inches, so do fulgurites also vary from one to two inches in diameter. They are generally less than 3 meters (9.8 feet) long, but can sometimes reach 20 meters (65.6 feet). Being so fragile, they are extremely difficult to excavate intact. As recognized by the Guinness World Records, the world’s longest fulgurite ever excavated measures a little over 4.9 meters (16 feet) and forks into three branches. Produced as a result of rocket-trigged lightning, it was unearthed in the grounds of Camp Blanding, near Starke, Florida, where the University of Florida maintains a lightning research facility in cooperation with the U.S. Army National Guard, called The International Center for Lightning Research and Testing (ICLRT).
Despite their fragility, fulgurites are highly resistant to weathering, and if left undisturbed can remain preserved in nature for many millions of years. A 250 million-year-old “fossil” fulgurite was found near the village of Corrie, on the Scottish isle of Arran, in 1966.
Scientific evidence shows that between 10,500 and 5,500 years ago, the Sahara was a very different environment to what it is today, being not a desert but a lush savannah where humans and animals thrived. In fact, we know the Sahara of the past was a lush savannah—and hence experienced lightning activity—on account of the large number of ancient fulgurites discovered there. Considered collectors’ items like precious stones or shells, fulgurites can be found for sale on such websites as eBay, many of these being of Sahara desert origin. These tend to be found when, as sand dunes are shifted by the wind, people spot them protruding from the sand.
Fulgurites, as we’ve seen, can remain preserved for a very long time. But just how valuable are they in terms of recording the past? The person best qualified to answer this question is Rafael Navarro-González, a chemist at the National Autonomous University of Mexico in Mexico City. In a study published in 2007, Navarro-González and his colleagues focused their attention on a very unique specimen of fulgurite. Collected from the Sahara in southwestern Egypt in 1999 and dated at 15,000-years-old, the scientists were attracted to the specimen on account of the fact that it contained embedded glass bubbles.
Using a laser to open the glass bubbles, Navarro-González was able to extract the gasses trapped inside them. The gasses were analyzed and found to contain traces of carbon dioxide, carbon monoxide, nitric oxide, and argon. Most intriguing of all was the high amount of carbon dioxide in proportion to argon, this being extremely dissimilar to what is present in a modern sample of Earth’s atmosphere.
So from where did this “extra” carbon dioxide originate? The researchers concluded that it must have been generated when the lightning bolt vaporized organic matter in the soil all those thousands of years ago. By measuring the ratio of carbon-12 to carbon-13 in the trapped gasses, it was discovered that the organic matter in question came from grasses and shrubs typical of hot, semi-arid environments, such as are found in southwestern Niger today, about 600 km (373 miles) south of the site where the fulgurite was discovered. Commented ScienceNews: “All these clues suggest that 15,000 years ago, near the end of the most recent ice age, the climate in southwestern Egypt was similar to that found today in Niger.”
The results of Navarro-González’s study constitute additional proof that the Sahara of the past was wetter than the Sahara of today. What’s more, the study demonstrates that a single fulgurite can yield a wealth of valuable scientific data pertaining to conditions on Earth in the past. However, fulgurites aren’t valued for scientific and aesthetic reasons only. According to some, they are more than just pieces of lightning-created glass; they are sacred objects whose powerful spiritual qualities can be put to use in prayer, meditation, healing, and so on. Those who subscribe to this notion see fulgurites as having captured the energy that fashioned them. “The lightning energy, long believed to be the touch of the Divine, still resides in them,” claims Robert Simmons in his book Stones of the New Consciousness.
Fulgurites can form in rock as well as sand. A typical rock fulgurite consists of a thin, glassy crust on the surface of the targeted rock. Since places of high elevation tend to draw lightning, we find, not surprisingly, that rock fulgurites are primarily found on mountain summits. I once came across a rock fulgurite while exploring the summit of a mountain in Tasmania, which consisted of a hole in the rock about one inch in diameter and about two inches deep. Around the hole was a dark, glassy coating. It was, as all fulgurites are, an impressive example of the awesome power of lightning.