NSRRC Activity Report 2022

Environmental and Earth Sciences 073 Secondary minerals were discovered locally on the glassy layer ( Fig. 1(b) ) and were identified as jarosite group minerals through in situ X-ray diffraction (XRD) at TLS 01C1 . Jarosite group minerals could indicate the presence of sulfate-bearing fluid and an acidic environment, which may be caused by rainwater. The local occurrence of jarosite group minerals implied that the alteration process requires not only rainwater but also high temperatures, i.e. , before the glassy layer completely cools to ambient temperature. The researchers therefore inferred that the jarosite group minerals were the hydrothermal alteration product of the scorched glass layer. This was the first study of natural fulgurite with recorded lightning current values. These values enable the estimation of fulgurite productivity by calculating the ratio between the energy required for the formation of fulgurite (E ful ) and the energy of the cloud-to-ground lightning event (E CG ). Therefore, Kuo applied the thickness of the glassy layer, the melted proportion results obtained using PXM and SEM, and the melting temperature of quartz of 1700 °C, in their calculations. The energy required for the formation of fulgurite was estimated to be approximately 2.1 MJ. Furthermore, the researchers employed a lightning-induced electrical heating model to calculate the total energy released by the cloud-to-ground lightning and obtained an estimate of approximately 8.1 GJ. Therefore, the estimated energy ratio (E ful /E CG ) was less than 0.03%. The study results indicate two possible explanations for the rarity of lightning-produced remnants in the geological record. The findings reveal that cloud-to-ground lightning dissipated a very small proportion of energy into the generation of fulgurite ( i.e. , less than 0.03% of the energy transferred to the surface), suggesting that rock fulgurite is difficult to produce. In addition, the thin glassy layers of exposed rock fulgurite are difficult to preserve due to intense physical weathering and chemical alteration, including the devitrification of glass into jarosite. Furthermore, the research team demonstrated that nondestructive, synchrotron-based analytical methods ( e.g. , PXM and XRD) are powerful and suitable tools for the analysis of rare samples formed under extreme conditions, such as meteorite impact, cloud-to-ground lightning, and earthquake rupture propagation. (Reported by Li-Wei Kuo and Tze Yuan Chen, National Central University) This report features the work of Li-Wei Kuo and his collaborators published in Contrib. to Mineral. Petrol. 177 , 111 (2022). TPS 21A X-ray Nanodiffraction TPS 31A Projection X-ray Microscope TLS 01C1 EXAFS • XRD, Laue Diffraction, PXM • Materials Science, Earth Science References 1. T. Y. Chen, L.-W. Kuo, D. Brown, J. Si, T.-J. Meng, H.-S. Sheu, Y.-F. Song, G.-C. Yin, Contrib. to Mineral. Petrol. 177 , 111 (2022). 2. L.-W. Kuo, S. A. F. Smith, C.-C. Chen, C.-S. Ku, C.-Y. Chiang, D. Brown, M. Negrini, W.-J. Huang, T.-Y. Chen, Sci. Rep. 11 , 22031 (2021).