Fulgurites are formed when lightning with a temperature of at least 1,800 °C melts silica or other common conductive and semiconductive minerals and substrates, fusing, vitrifying, oxidizing and reducing mineral grains and organic compounds; the fulgurite mass is the rapidly-quenched end-product.
The temperature peak within a lightning channel, however, is known to exceed 30,000 K, with sufficient pressure to produce planar deformation features, or "shock lamellae" in SiO2 polymorphs.
It is assumed that the process of forming a fulgurite occurs over a timespan of the order of a single second, following the termination of the return stroke sequence, and leaves direct evidence of the dissipation path and its dispersion over the surface or into the earth.