^1,2,3M. R. Boyd,^1,2M. J. Genge,⁴A. G. Tomkins
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70123]
¹Department of Earth Science and Engineering, Imperial College London, London, UK
²Natural History Museum, London, UK
³Grantham Institute – Climate Change and the Environment, Imperial College London, London, UK
⁴School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
Published by arrangement with John Wiley & Sons

Natural microspherules are formed by high-temperature processes and are present throughout the geologic record to the present day. We report the discovery of large numbers of microspherules recovered from a rock pavement in the Pilbara region, Western Australia. Textures range from glassy to coarse-grained, with many particles containing crystallites, vesicles, and relict grains. Compositions are non-chondritic and are either dominated by silicates or Fe-Ti-bearing oxides. Spherule and relict grain compositions show strong affinities to the mineralogy of the underlying rock, a Paleoarchean granite gneiss. Bulk compositions suggest formation by a localized melting process with precursors dominated by individual pre-existing minerals, with minimal mixing. Numerical modeling of the formation of spherules suggests formation by rapid quenching, possibly from melt droplets. Modeled cooling times are consistent with compositions that indicate limited evaporation. The compositions and textures of these spherules are not compatible with either microtektites formed by meteor impact or micrometeorites formed by the atmospheric entry of cosmic dust and are instead interpreted to have formed via lightning strikes. Spherules generated by lightning strikes may be present in the geologic record and thus could be used as a paleoclimate proxy where other signatures, such as main mass fulgurites, have not survived.

¹Neeraj Srivastava et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70121]
PRSS, PSDN, Physical Research Laboratory, Ahmedabad, India
Published by arrangement with John Wiley & Sons

Estimating mineral abundance in meteorites provides crucial information about the early solar system and planetary formation processes. This study presents a new empirical approach for the estimation of modal abundance of olivine (Ol), high-calcium pyroxene (HCP), and low-calcium pyroxene (LCP) using band area ratio (BAR), a spectral parameter derived using reflectance spectroscopy. Using spectral data of 22 mineral mixtures acquired from the RELAB spectral library, the BAR values were initially calculated. These BAR values were then plotted against Ol% and HCP%, and based on the trends observed, a set of equations was formulated to get the initial estimate of mineral abundances. To apply these to actual samples, an error reduction framework has been developed that involves determination of a class-specific correction factor (CF) for H, L, and LL types of ordinary chondrites (OCs) to account for the presence of other minerals, metals, and impurities. The CF is a quantitative adjustment that is subtracted from the initial estimates to align calculations with the actual values. After application of the CF, the 1σ uncertainties associated with the abundance estimates were found to be ±1.85% for Ol, ±0.91% for HCP, and ±1.63% for LCP. The study demonstrates the estimation of the mineral abundances of seven OCs, using spectral analysis conducted at the Planetary Remote Sensing Laboratory (PRSL), Physical Research Laboratory (PRL). The proposed approach is robust even for bulk samples analyzed under different viewing geometries and provides a rapid, nondestructive alternative to traditional techniques for mineral abundance estimation in meteorites, planetary samples, and analogs.