They are formed when lightning with a temperature of at least 1,800 °C (3,270 °F) instantaneously melts silica on a conductive surface and fuses grains together; the fulgurite tube is the cooled product. This process occurs over a period of around one second, and leaves evidence of the lightning path and its dispersion over the surface. Fulgurites can also be produced when a high voltage electrical distribution network breaks and the lines fall onto a conductive surface with sand beneath. The glass formed is called Lechatelierite which may also be formed by meteorite impact and volcanic explosions.