When lightning hits an area with lots of silica in the surface material such as sand, the material may fuse and create a lightning rock – known as a fulgurite. The tempereature inside lightning can go up to 30 000 Kelvins (29 700 degrees celsius), instantly melting and fusing the sand.
Most often, the fulgurite is tube-shaped with a hollow interior. The insides of fulgurites are often glassy and smooth, due to the rapid cooling of the fulgurite after being hit by the lightning. If the fulgurite is not tube-shaped, it is called an exogenic fulgurite, which is when the material is thrown into the air during a lightning strike and then melted and fused.