Lunar Soil - Mineralogy and Composition

Mineralogy and Composition

Lunar soil is composed of various types of particles including rock fragments, mono-mineralic fragments, and various kinds of glasses including agglutinate particles and volcanic and impact spherules. The agglutinates form at the lunar surface by micrometeorite impacts that cause small-scale melting which fuses adjacent materials together with tiny specks of metallic iron (Fe0) embedded in each dust particle’s glassy shell.

Over time, material is mixed both vertically and horizontally (a process known as "gardening") by impact processes. However, the contribution of material from great distances is relatively minor, such that the soil composition at any given location largely reflects the local bedrock composition.

There are two profound differences in the chemistry of lunar regolith and soil from terrestrial materials. The first is that the Moon is very dry. As a result, those minerals with water as part of their structure such as clay, mica, and amphiboles are totally absent from the Moon. The second difference is that lunar regolith and crust are chemically reduced, rather than being significantly oxidized like the Earth's crust. In the case of the regolith, this is due in part to the constant bombardment of the lunar surface with hydrogen (H) from the solar wind. One consequence is that iron on the Moon is found in the metallic 0 and +2 oxidation state, whereas on Earth iron is found primarily in the +2 and +3 oxidation state.