Particle track record of Apollo 15 green soil and rock.
Track densities, track stability, and uranium contents have been measured in lunar samples containing abundant green glass spherules from stations 6a and 7 of the Apollo 15 mission. This glass is rather homogeneous in its track registration properties but nonuniform in its uranium content, specific gravity, and bulk etching rate. The major components of a soil sample, 15401, are found to have had an unusually short surface exposure (500,000 yr) and to have been stirred at least once, but not often during its lifetime. A nearby soil clod, 15426, appears to have been brought to the surface in the same event. 15405, the rock upon which 15401 was perched, has recorded deformation features and track densities compatible with its surface residence having begun at the same time.