Fulgurites (from the Latin fulgur, meaning "thunderbolt”). They are natural hollow glass tubes often formed during lightning strikes, in quartzose sand, silica, or soil. Sometimes they are referred to as petrified lightning.Fulgurites are formed when lightning with a temperature of at least 1,800 °C (3,270 °F) melts silica on a conductive surface and fuses mineral grains together; the fulgurite tube is the cooled product. This process occurs over a timespan of around one second.

Fulgurites

Fulgurites