Fulgurites (also "flash tube" or "petrified lightning")
Lightning strikes cannot only burn trees. When striking ground, sometimes the extreme heat even melts soil or sand. Along its path natural glass tubes or other weird structures are formed. These "petrified lightnings" are a very rare phenomenon and are particulary found in desert regions. Some have a length up to 4 meters but they are very fragile and just fragments of few centimers are found.
Some of the fulgurites or "flash tube" you can buy in our shop were picked with our own hands in the Sahara desert, the rather white ones originate from Florida.