A Geochemical Analysis of Fulgurites: from the inner glass to the outer crust

Cloud-to-ground lightning strikes produce natural glasses on the surface of the Earth, called fulgurites. These natural glasses are tubular in shape with a central void surrounded by an inner glass, and the inner glass is surrounded by an outer crust or toasted region. Previous studies report different kinds of melts existing in several different types of fulgurites; however, little to no chemical data has been collected that tracks chemical variations from the inner glass to the outer crust of a fulgurite. This study uses microprobe and laser ablation inductively coupled plasma mass spectrometer analytical techniques to collect transects of chemical composition from the inner glass to the outer crust of eleven fulgurites. Five of the eleven fulgurite samples show a well-mixed, volatile-depleted inner glass, enclosed in a poorly mixed volatile enriched outer melt, suggesting that these fulgurites formed from the vaporization and condensation of materials on the inner fulgurite wall. The remaining six fulgurites show poorly mixed melts in both the inner glass and outer crust regions, and most likely originated as lightning-produced melting phenomena. These data suggest that certain enigmatic natural glasses, such as Edeowie, Dakhleh and other unknown desert glasses, may be lightning-produced, in contrast to the meteorite burst or impact related origins that have commonly been propounded