Lunar soil

Lunar soil is the fine fraction of the regolith found on the surface of the Moon. Its properties can differ significantly from those of terrestrial soil. The physical properties of lunar soil are primarily the result of mechanical disintegration of basaltic and anorthositic rock, caused by continuous meteoric impact and bombardment by interstellar charged atomic particles over billions of years. The process is largely one of mechanical weathering in which the particles are ground to finer and finer size over time. This situation contrasts fundamentally to terrestrial soil formation, mediated by the presence of molecular oxygen (O₂), humidity, atmospheric wind, and a robust array of contributing biological processes. Some have argued that the term "soil" is not correct in reference to the Moon because on the Earth, soil is defined as having organic content, whereas the Moon has none. However, standard usage among lunar scientists is to ignore that distinction.

The term lunar soil is often used interchangeably with "lunar regolith" but typically refers to only the finer fraction of regolith, that which is composed of grains one cm in diameter or less.Lunar dust generally connotes even finer materials than lunar soil. There is no official definition of what size fraction constitutes "dust", some place the cutoff at less than 50 micrometres in diameter, others at less than 10.