Regolith covers almost the entire surface of the Moon
The lunar “soil” is the finer fraction of the regolith and has almost entirely been the result of billions of years of meteor and micro-meteoroid impacts on the surface.
These impacts disintegrate basaltic and anorthositic rock, which is progressively ground finer and finer over time by successive impacts
Solar and galactic charged particles also does some breaking down as well.
Average depth of regolith:
generally 4-5 meters thick in the mare areas
generally 10-15 meters thick in the older high land regions
Below the regolith: blocky bedrock, fractured over time by larger meteor impacts
Gradations of Regolith
Very roughly speaking, there are a few grades of regolith
lunar dust: less than 30 micrometers in diameter
lunar soil: 1 centimeter in diameter or less
lunar regolith: everything else
Composition of Lunar Regolith
Formation Processes
Comminution: mechanical breakdown of rocks and minerals into smaller particles by meteor and micrometeorite impacts.
Agglutination: welding of mineral and rock fragments together by micrometeorite impact produced glass
Solar wind sputtering and cosmic ray spallation: caused by impact of ions and other high energy particles
Fire fountaining: older process whereby volcanic lava is spewed and cool into small glass beads before falling back to the surfac
orange dirt at Shorty Crater found by Apollo 17
green glass at Hadley-Apennine found by Apollo 15
Deposits of volcanic beads also though to be the orgin of dark mantle deposits (DMD) at other locations
