Formation of Apollo 17 orange and black glass beads

Abstract

Size frequency distributions of the cross sections of orange and black glass beads in the 125–250 µm fraction of soil 74220 have been determined. Cross section medians of black vitrophyric and orange glassy beads in the 125–250 µm fraction are 0.16 mm and 0.14 mm, respectively. The vitrophyric beads contain skeletal olivine crystals mantled by ilmenite. Some beads contain fragments and euhedral crystals of endogeneous olivine. “Free‐flight” cooling rates and the critical cooling rate for crystallization have been determined with a synthetic melt of orange glass composition. The critical cooling rate is approximately 100° C/s. The “free‐flight” cooling rate of droplets 0.16 mm in diameter is approximately 1080° C/s. It is inferred that Apollo 17 orange melt droplets were erupted together with a large mass of hot gas and/or formed a dense cloud of heat‐radiating droplets.