No abstract

With reflectance spectroscopy, one is measuring only properties of the fine‐grained regolith most affected by space weathering. The Lunar Soil Characterization Consortium has undertaken the task of coordinated characterization of lunar soils, with respect to their mineralogical and chemical makeup. It is these lunar soils that are being used as “ground truth” for all airless bodies. Modal abundances and chemistries of minerals and glasses in the finest size fractions (20–45, 10–20, and <10 μm) of four Apollo 14 and six Apollo 16 highland soils have been determined, as well as their bulk chemistry and IS/FeO values. Bidirectional reflectance measurements (0.3–2.6 μm) of all samples were performed in the Reflectance Experiment Laboratory. A significant fraction of nanophase Fe0 (np‐Fe0) appears to reside in agglutinitic glasses. However, as grain size of a soil decreases, the percentage of total iron present as np‐Fe0 increases significantly, whereas the agglutinitic glass content rises only slightly; this is evidence for a large contribution to the IS/FeO values from the surface‐correlated nanophase Fe0, particularly in the <10 μm size fraction. The compositions of the agglutinitic glasses in these fine fractions of the highland soils are different from the bulk chemistry of that size; however, compositional trends of the glasses are not the same as those observed for mare soils. It is apparent that the glasses in the highland soils contain chemical components from outside their terrains. It is proposed that the Apollo 16 soils have been adulterated by the addition of impact‐transported soil components from surrounding maria.

Abstract-Geothermometry based on the compositions of clinopyroxenes in type 6 and 7 LL chondrites gives coherent results, but the estimated temperatures from coexisting orthopyroxenes are consistently lower than for clinopyroxenes. Orthopyroxene thermometry is suspect because of compositional effects of polymorphic inversions and/or unknown kinetic factors. Lack of clinopyroxene equilibration precludes accurate estimation of peak metamorphic temperatures for type 4 and 5 chondrites. There is no apparent correlation between Al content (a pressure-dependent variable) and equilibration temperature in chondritic pyroxenes. This finding, which is at variance with a previously published conclusion that temperature and pressure are correlated in metamorphosed chondrites, may have important implications for asteroid thermal models.