Fulgurites ("petrified lightning")

Lightning strikes cannot only burn trees but sometimes the extreme heat can also melt soil or sand. Along its path natural glass tubes or other weird structures are formed. These "petrified lightnings" are a very rare phenomenon and can be found e.g. in desert regions. Some have a length up to 4m, but they are very fragile and can mostly extracted in fragments.
Some of the offered fulgurites (some call them "flash tube") are found by ourselves in the Sahara, others (e.g. the white ones) originate from Florida.