These are tubular-shaped structures that appear when lightning strikes the sand of a beach or desert, although it can also occur in siliceous rocks . Upon contact with the ground, the electromagnetic pulse increases the temperature of the sand until it melts (it can exceed 1,800 ºC).
The discharge of electricity is capable of penetrating more than a meter in depth and, as if it were conductive wire, melt the grains of sand around it, leaving fine hollow cylinders between 2 and 50 mm in diameter. Twisted, branched and joined tubes can also be found to form larger structures or as part of rocks.
The interior of fulgurites is usually smooth, but sometimes it has tiny bubbles, and the exterior is covered by grains of sand that have not melted due to the effect of heat. The material resulting from the liquefaction and subsequent solidification of the sand or sandstone particles is vitrified silica or lechatelierite. It is usually dark, but there are also shades of bronze, green and white. They look like a small root or narrow stem , but are rougher to the touch.
Scientists can produce vitrified silica in a laboratory, however finding them in nature is not easy. They can be found in deserts such as the Sahara, but they are rare due to the rare phenomenon that originates them. Their name comes from fulgur, 'lightning' in Latin, and they are also called by the name of petrified lightning. In New Jersey, one of the largest known was collected, measuring 2.74 meters.
