The role of very fine particle sizes in the reflectance spectroscopy of plagioclase-bearing mixtures: new understanding for the interpretation of the finest sizes of the lunar regolith

1Giovanna Serventi, 2Cristian Carli
Icarus (in Press) Link to Article [http://doi.org/10.1016/j.icarus.2017.04.018]
1Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Viale delle Scienze 157/A Parma 43124, Italy
2IAPS-Inaf, Viale Fosso del Cavaliere Tor Vergata, Roma, 00133 Italy
Copyright Elsevier

The lunar surface consists of a regolith layer that covers the underlying bedrocks, and is generally characterized by particulates

The coarsest sizes of the regolith are chemically and mineralogically similar, while the finest fractions are more feldspathic, probably due to easier fracturing of plagioclase than mafic minerals.

Due to the more feldspathic nature of the very fine lunar soils, in this paper, we quantitatively investigate the influence of very fine (

(1) fine sizes act principally on reflectance and on spectral contrast (with the former increasing and the latter decreasing); (2) very fine plagioclase has a blue slope in the Near Infrared and very shallow 1250 nm band depth, close to zero; (3) consequently, the plagioclase band is always shallower than mafic bands; (4) in mixtures with olivine, the composite band center always shows the typical olivine value, differently from coarser mixtures; and (5) mafic materials have a blue slope in the Short Wavelength Infrared Region, a more V-shaped 1µm pyroxene absorption and the 1µm mafic band centers are shifted by ca. 40 nm vs. coarse sizes, reflecting a different weight within the crystal field absorption of the mafic component in very fine size. We also evidenced that a coarse plagioclase could be overestimated, while a very fine one could be underestimated if compared with the 63-125µm size.

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