Regolith

Image taken during the mission Apollo 16

Regolith (from the Greek ῥῆγος rhēgos 'blanket [colorful]' and λίθος líthos 'stone') is the general term used for designate the layer of unconsolidated, altered materials, such as rock fragments and mineral grains, that rests on solid undisturbed rock. It reaches its maximum development in the humid tropics, where depths of several hundred meters of altered rock are found. Its lower limit is the weathering front.

Regolith is also defined as the continuous layer of fragmentary, incoherent material, produced by meteoritic impacts, which normally forms surface deposits on planets, satellites and asteroids where the atmosphere is thin or absent; the classic example is lunar regolith, several meters thick, with components ranging from metric-sized blocks to microscopic dust and glass particles.

Moon regolith

The lunar surface is covered by regolith, which can be defined as that carpet of remains made up of loosely compacted materials of rocky fragments and soil, all covering a solid rocky bottom. Conventionally, it has been established that all those particles with a diameter of less than one centimeter are called "soil", while larger particles are called "rocks".

The lunar regolith can have different origins: the bombardment of meteorites and micrometeorites, solar radiation, the great variation in temperatures between day and night, or erosions produced by different causes. Its texture is reminiscent of wet sand and it adheres strongly to clothing, its hue is dark, and its smell is similar to burning gunpowder (although the smell is probably due to the oxidation of lunar dust upon contact with the oxygen present). inside the astronauts' probes).

It seems that the average depth of the regolith in the areas of the lunar seas reaches four or five meters, while in the areas corresponding to the mountainous regions it can reach ten or even more meters. It is made up of basalts, which are very fine-grained, dark igneous lunar rocks, consisting primarily of feldspar, plagioclase, and pyroxenes, with or without olivine and other minerals, as well as one to two percent meteoritic material from outer space.

Anorthosite is basically composed of plagioclase. Pyroxene is the most common mineral in the rocks of the seas, and is a yellowish-brown calcium-magnesium-iron silicate. Olivine is a magnesium-iron silicate that occurs as pale green crystals.

In lunar seas, the rock fragments are basalts, composed of pyroxene, plagioclase and other minerals, while in mountainous areas the fragments are basically rocks rich in plagioclase and broken plagioclase crystals.

Another mineral located on the lunar surface is armalcolite, an oxide of titanium with iron and magnesium that forms opaque crystals, named after the three Apollo 11 astronauts (Armstrong, Aldrin and Collins).

The age of the regolith has been estimated at 3.8 to 4.0 billion years.

In some texts a translation from English or German can be found in the feminine form (regolith). "Consequently, gas-rich meteorites must have formed in the regolith (that is, the dust layer of the lunar surface)."