Petrogenetic insights from textural complexity of lunar glass beads

Lunar glass beads include spherules, dumb-bells, bars, and irregular glass-rich objects that are typically tens to hundreds of micrometres across and occur in lunar soil at all known landing sites. Lunar glass beads preserve a wide range of glass compositions and ages and are considered to represent quenched molten droplets that are ballistic ejecta from impact cratering events (impact glasses) and/or eruptive volcanic lava fountain products (volcanic glasses). As such, studying glass beads can provide insights into the volcanic and impact history of the Moon. This study investigates the textural complexity of lunar glass beads from various Apollo landing sites revealed by backscatter electron (BSE) imaging and electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) mapping. Individual beads show a wide range of textures, with variable digestion of remnant mineral and lithic clasts, compositional inhomogeneity of the glass, sizes and abundance of vesicles, immiscible Fe-metal melt droplets, and nucleation and growth of neoformed porphyritic phases or crystalline matrices within the melt droplet. The wide range in textures is explained in terms of differences in the initial composition of the target rock (impact glasses) or magma (volcanic glasses), initial melt temperature, physical mixing, and cooling rate of the beads.