Fulgurite

Named from the Latin fulgur, meaning lightning, fulgurites are the result of lightning striking something terrestrial. They can form in any type of easily melted rock, but most are found in desert regions where quartz-laden sand has been melted and surrounding loose material has eroded away. The heat of the lightning melts the quartz into glass tubes, some branching out like trees, lined with fused or partially melted sand on the outside. Fulgurites are found worldwide.