Fulgurite

By Alex Scott

Since the beginnings of civilization, humans across cultures have marveled at the power and mystery of the natural phenomenon known as lightning. Although we know now that lightning comes from the release of electrostatic energy in the air and not from Zeus or Thor or Indra, we still can’t help but find lightning fascinating. And one of the most interesting aspects of this phenomenon is the traces it leaves behind. 

When a lightning bolt hits an open patch of sand or a high mountain peak, it can create a structure known as fulgurite, from the Latin “fulgur” or lightning. In fact, the ancient Roman philosopher Cicero wrote the expression “condere fulmina” or “dig up thunderbolts,” suggesting that even then, the Romans were aware of and studied these physical remnants left behind by lightning bolts. 

Fulgurite is broadly categorized into two types, sand and rock, depending on its composition. A lightning bolt heats the air around it up to 50,000 degrees Fahrenheit, 5 times hotter than the sun’s surface, and discharge up to 100 million volts into the ground. This intense heat and electric potential instantaneously melts whatever materials have been hit and forms a hollow tubular shape.

Depending on the composition of the sand or rock, the color and texture of fulgurites can vary, although they generally have white to black coloring and rough, bumpy exteriors. They also vary in length, which is determined by the power of the bolt and the density of the struck material. Paleolightning, or the study of lightning throughout history, uses these differences in ancient fulgurites to ascertain the composition of the Earth’s surface through time.

Whether you’re interested what fulgurite can tell us about the past or just adding it to your collection, a beach thunderbolt is a rare natural marvel that will continue to fascinate humans for millennia.

Learn more about beach rocks:

Learn more about beach rocks including agates, Cape May diamonds, Yooperlites, fulgurite, puddingstone, and more. Articles ›

This article appeared in the Beachcombing Magazine March/April 2020 issue.