Lightning stones, also known as fulgurites, are formed when lightning strikes the ground, fusing and vitrifying mineral grains. The heat of the lightning bolt vaporizes the center of the fulgurite, leaving it with a tubular form. The primary SiO 2 phase in common tube fulgurites is lechatelierite, an amorphous silica glass. Fulgurites are considered to be among the more rare occurring rocks. ^{wikipedia.org 1 2 3 4 5}