When lightning strikes the ground, the intense heat of the current can melt dry sand and create glass. Sometimes, this happens along the path of the lightning itself, leaving a hollow, branching tube of rough, sand-caked glass where the lightning traveled. The interior of the tube is usually very smooth. Such fragments of petrified lightning are known as fulgurites. They can form deep below the surface that was struck or, more rarely, above it. How long is the longest fulgurite ever found? Discuss