These are impact-produced craters (~5 microns in diameter) on a lunar glass bead from the soil. The rule of thumb is that the size of the projectile is about 1/10th that of the diameter of the crater it produces. Thus, the size of the micrometeorite was about 0.5 microns (1/100th the diameter of a hair on your head).
(7 of 42 slides)
Comminution and agglutination are the major processes involved in the formation of lunar soils. The other two processes are only of local importance.
(8 of 42 slides)
Micrometeorites impact the lunar soil, some with enough energy to melt the silicate minerals. This melt splashes over grains, quenches to glass, and forms agglutinates. Some melt reaches even higher Ts and partially vaporizes, only to condense on the surfaces of other grains.
(9 of 42 slides)
