How Can Lightning Turn Sand Into Glass?

A brief burst of concentrated heat

A lightning discharge deposits energy along a narrow path. In suitable sand, this can heat the mineral grains enough to melt them. The surrounding grains may partly fuse while the material nearest the channel is more strongly transformed. ^[1]

Cooling preserves a branching path

As the molten material cools, it solidifies into glass. Sand fulgurites can have a hollow center and branches that follow the discharge through the ground. Their shape depends on the lightning path and ground conditions, so no two specimens need look alike. ^[2]

Natural glass does not have to look clear

A fulgurite is often rough, dark, and covered in attached grains. Its glassy inner surface may be easier to recognize than its exterior. A lightning strike can also form glassy coatings or veins on rock, rather than a long tube in loose sand. ^[2]

Why every strike leaves no obvious tube

Finding a fulgurite requires suitable material, enough concentrated energy, and preservation after formation. The tubes can break easily, and many remain buried. Their absence at the surface does not prove that an area has never been struck by lightning. ^[1]

Keep exploring: why cooling lava forms basalt columns.