Fulgurite

The fulgurites (from Latin fulgur, 'lightning') are the result of the lightning strike on sandy ground, causing the fusion of silica grains, crystallizing in the form of ray tubes. It is typical of sand deserts and coastal dunes. They are mainly made up of lechatelierite (silica glass, considered a mineraloid, since being a glass it has an amorphous, non-crystalline structure, although it is often classified in the group of quartz minerals).