Rapid Raman mapping of a fulgurite
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A fulgurite is a naturally occurring glass formed when lightning hits sand, rock, or soil. The formation of fulgurites is accompanied by mineralogical and sometimes compositional changes, and may record information about the environment in which they were formed. A previous investigation using Raman point spectroscopy discovered the presence of anatase, a low-temperature polymorph of TiO2, and polyaromatic hydrocarbons within a fulgurite. These findings indicate that there were regions within the sample that were not subjected to temperatures of 2,000 K or more that the matrix is reported to attain when struck by lightning. This paper seeks to expand the previous research by utilizing the capabilities of a new Raman spectroscopic technological development that enables rapid mapping. The entire surface area of a cross-sectioned fulgurite (∼40 mm × 23 mm) sample was mapped allowing several regions of polyaromatic hydrocarbons and anatase to be located. Furthermore, shocked quartz was found within the boundary regions of the fulgurite, and is proposed to have resulted from contact with vaporized material during the lightning strike. Shocked quartz is typically indicative of extraterrestrial impact, yet its discovery here suggests that its formation is not exclusive to the impact process.
KeywordsRaman spectroscopy Rapid mapping Fulgurite Shocked quartz
This research was supported by the Australian Research Council (International Linkage and LIEF grants), as well as the USYD/NHMRC Major Equipment Funding Scheme, and grant NNX07AU08G from NASA Exobiology and Evolutionary Biology (MAP). The authors are grateful to Virginia Pasek who developed the program to solve the thermal diffusion equation. EAC would like to thank Sarah Kelloway for brainstorming, reading and editing this manuscript, and her photographic skills. The authors also acknowledge the facilities as well as scientific and technical assistance from staff in the AMMRF (Australian Microscopy & Microanalysis Research Facility) at the Electron Microscope Unit, The University of Sydney.
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