Mossbauer mineralogy on the Moon: The lunar regolith

A first-order requirement for spacecraft missions that land on solid planet ary objects is instrumentation for mineralogical analyses. For purposes of providing diagnostic information about naturally-occurring materials, the e lement iron is particularly important because it is abundant and multivalen t. Knowledge of the oxidation state of iron and its distribution among iron -bearing mineralogies tightly constrains the types of materials present and provides information about formation and modification (weathering) process es. Because Mossbauer spectroscopy is sensitive to both the valence of iron and its local chemical environment, the technique is unique in providing i nformation about both the relative abundance of iron-bearing phases and oxi dation state of the iron. The Mossbauer mineralogy of lunar regolith sample s (primarily soils from the Apollo 16 and 17 missions to the Moon) were mea sured in the laboratory to demonstrate the strength of the technique for in -situ mineralogical exploration of the Moon. The regolith samples were mode led as mixtures of five iron-bearing phases: olivine, pyroxene, glass, ilme nite, and metal. Based on differences in relative proportions of iron assoc iated with these phases, volcanic-ash regolith can be distinguished from im pact-derived regolith, impact-derived soils of different geologic affinity (e.g., highlands and maria) can be distinguished on the basis of their cons tituent minerals, and soil maturity can be estimated. The total resonant ab sorption area of the Mossbauer spectrum can be used to estimate total FeO c oncentrations.