SEM ANALYSIS OF FULGURITE FORMED ON QUARTZITE, WHITE MOUNTAINS, CALIFORNIA

Fulgurite is a glassy rock formed by flash melting when lightning strikes soil. Temperatures exceeding 2000K rapidly melt the soil to create a glassy, vesicular, tube-like structure a few cm in diameter. Here we report scanning electron microscope analysis of a fulgurite sample from the White Mountains of California. Understanding how electric current melts soil, such as in fulgurite, is essential for developing better methods of environmental rehabilitation such as in situ vitrification (ISV), which is used to stabilize hazardous waste in contaminated soil.

The sample of fulgurite we examined formed when lightning struck power lines at an altitude of 3,300 m, causing extensive melting of the underlying soil, which is composed of fine-grained, magnetite-rich quartzite of the Cambrian Campito Formation. The fulgurite is surrounded by an exterior of unmelted soil and quartzite pebbles; we speculate that the electric current was able to easily spread through the conductive soil, made damp in this desert environment by rain during the thunderstorm, whereas the pebbles were nonconductive and did not melt as easily. In the fulgurite there are two variants of glass, with sharp boundaries between the unmelted quartzite and the glass. The majority of the glass is felsic, containing abundant Na, K, Al, and Si, most likely from melted alkali feldspar, clay, and quartz, minerals found in a soil sample obtained from the base of the mountain. Fe and Ti-rich minerals, such as ilmenite, are present in both the soil and fulgurite samples, but 38% of spot analyses of the Fe-Ti rich areas have significant concentrations of SiO2 and Al2O3, signifying that the substance is a glass.