An Etymological Dictionary of Astronomy and Astrophysics

A fine, powder-like dust covering the Moon’s surface. → regolith. It is formed when meteoroids crash on the Moon’s surface, heating and pulverizing rocks, which contain silica and metals. Since there is no wind or water to smooth rough edges, the tiny grains are sharp and jagged, and cling to nearly everything. Their main chemical compositions are SiO₂ (about 45%) and Al₂O₃ (about 15%).
The dust grains have an average size of 19 microns (40% smaller than hair).

See also: → lunar; → dust.