SOURCE IDENTIFICATION OF QUARTZ IN INTERMEDIATE ANTHROPOGENIC FULGURITES, SPOKANE COUNTY, WA

In July 2022 a copper electric distribution wire fell on sandy basecourse and pulsed about for about an hour causing a line of artificial, or anthropogenic fulgurites. These glass tubes were excavated, described, and analyzed using multiple methods to relate to fulgurites formed from lightning strikes (natural fulgurites). The clastic material that melted was about 60 percent basalt gravel to sand and 40 silica-dominated sand from local Pleistocene megaflood deposits. The resulting glass is about 60 wt% SiO2 from microprobe analyses. Using a single crystal diffractometer with Mo radiation at Whitworth results of analysis of clear to white minerals correlate closest to alpha-quartz (a low temperature variation of quartz) and amorphous silica. Solid State NMR resulted in a broad glass pattern with a minimal peak for 29Si. Thin section analyses showed quartz crystals surrounded by lighter colored glass, vesiculation, and disequilibrium textures and dissolution profiles with decreasing wt% SiO2 trending away from the minerals into the melt. Though fulgurites have been found with cristobalite and stishovite mineralization, the fulgurites from Four Lakes, WA contained amorphous silica and alpha-quartz likely resulting from melting of host quartz and not crystallization from the melt. The lack of crystal formation in the artificial fulgurite is attributed to the pulsing of the downed electric line and an intermediate melt chemistry.