Occurence and Sources of Aluminum on the Moon

Aluminum composes 10% of the atoms and 13% of the mass of lunar highland regolith, being the third most abundant element. In the mare basins, aluminum makes up only 4.5% of the atoms and 5% of the weight, strongly suggesting the use of highland feedstocks for aluminum extraction.

Plagioclase is the carrier of nearly all the Al in the lunar crust, rather than bauxite as on Earth. Plagioclase feldspar includes anorthite (CaAl₂Si₂O₈), and far smaller amounts of albite (NaAlSi₃O₈). Anorthosite is generally over 90% plagioclase, while norite has about equal proportions of plagioclase and low-calcium pyroxene, and troctolite consists of plagioclase and lesser amounts of olivine. These rocks are the principal constituents of the highland regolith and are all potential ores.

Aluminum has a strong negative correlation in concentration with iron. In fact, the correlation between aluminum and the combined iron and magnesium concentrations is almost linearly negative. In samples where combined magnesium and iron concentrations are very small, aluminum concentrations are around 30-35%, and aluminum concentrations drop to their minimum of about 5-10% in samples with combined iron and magnesium concentrations at a mean of about 30%.

In highland rocks, a concentration of iron below 4% virtually guarantees aluminum concentrations from 25 to 35%. As iron is magnetic, this suggests a possible approach for magnetically evaluating rocks or bulk ores for aluminum extraction.

Aluminum also has a clear positive correlation with calcium, linear between samples with about 20% aluminum and 12% calcium to samples with about 35% aluminum and 20% calcium.