¹T.A. Williams, ¹S.W. Parman, ¹A.E. Saal, ²A.J. Akey, ²J.A. Gardener, ³R.C. Ogliore
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116607]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, United States of America
²Center for Nanoscale Systems, Harvard University, Cambridge, MA, United States of America
³Department of Physics, Washington University in St. Louis, St. Louis, MO, United States of America
Copyright Elsevier

Lunar pyroclastic glass beads preserve a record of physical and chemical conditions within volcanic gas clouds in the form of nanoscale minerals vapour-deposited onto their surfaces. However, the scale of these mineral deposits – less than 100 nm – has presented challenges for detailed analysis. Using SEM, TEM, APT, and NanoSIMS, we analysed pristine glass beads from Apollo drive tube 74,001 and found a sequence of sulfide deposition that directly evidences lunar gas cloud evolution. The deposits are predominantly micromound structures of nanopolycrystalline sphalerite ((Zn,Fe)S), with iron enrichment at the bead-micromound interface. Thermochemical modelling indicates that hydrogen and sulfur were major elements within the volcanic plume and ties the iron gradient to decreasing gas pressure during deposition. This pressure drop may also be consistent with our observed trend of potential
depletion. Finally, Apollo 1,774,220 orange beads, deposited higher in the Shorty Crater sequence, appear to lack abundant ZnS nanocrystals (Liu and Ma, 2024a), suggesting a change in vapour deposition between black- and orange-glass bead deposition. Together, our results suggest a change in eruption style over the course of a pyroclastic volcanic eruption in the Taurus-Littrow Valley.