Ferromagnetic resonance intensity: A rapid method for determining lunar glass bead origin

Abstract

Ferromagnetic resonance intensity (IS) was tested as a criterion for use as a nondestructive, reliable, and rapid screening method for distinguishing volcanic from impact glass spherules in the lunar soils. This method relies on the absence or presence of single‐domain Fe formed during impact melting by autoreduction of Fe2+ in the melt. Extensive scanning electron microscope (SEM) inspection of individual glass bead surfaces provided reliable evidence of the mode of glass genesis. Ferromagnetic resonance intensity was tested against the ‘type’ Apollo 15 and Apollo 17 volcanics. Additional volcanics were also found during the course of the study. Ninety‐four percent of the volcanic glasses had IS values less than one, implying the absence of single‐domain Fe. Seventy‐five percent of impact glasses had elevated IS values. The remaining impact beads had IS values less than one. These samples lack single‐domain Fe and could represent impact melts of bedrock with little or no regolith contribution. The ability to discriminate bedrock‐derived impact melts as opposed to impact melts partially or completely derived from regolith, and the primary discrimination of volcanic glasses from impact glasses, suggests the FMR technique can be important in determining the origin of lunar glass spheres.