Vapor Condensates on the Most Pristine Black Beads From a Clod in Apollo Drive Tube 73001: Discovery of Lunar NaCl Nanocrystals

Identification of the mineral species of vapor condensates on the surface of lunar pyroclastic beads, formed during the flights of beads in the lunar volcanic plume, helps to constrain the physical and chemical conditions of the lunar volcanic plume. We conducted nanomineralogy studies of vapor condensates on the surface of pristine black beads from a clod that was extracted from the recently opened Apollo drive tube 73001. This drive tube had been sealed under vacuum since its collection on the Moon and thus represents the most pristine sample in allocatable Apollo collection. Vapor condensates observed on the surface include patches made of ZnS nanocrystals and possible rare scattered NaCl nanocrystals. ZnS nanocrystals were previously found on Apollo 15 green and yellow beads, but NaCl nanocrystals are unique to black beads. Both ZnS and NaCl nanocrystals are absent in Apollo 17 74220 orange beads. Although orange and black beads are of similar chemistry, black beads in the clod 73001, 226 could form from a different environment.