VIS-IR study of brucite–clay–carbonate mixtures: Implications for Ceres surface composition

• Published in: Icarus (New York, N.Y. 1962) Vol. 280; pp. 315 - 327
• Main Authors: De Angelis, S., Manzari, P., De Sanctis, M.C., Ammannito, E., Di Iorio, T.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.12.2016
• Subjects: Absorption; Asteroid Ceres; Brucite; Carbonates; Ceres asteroid; Clay minerals; Magnesium hydroxide; Mineralogy; Minerals; Spectra; Spectroscopy; Spectroscopy; Asteroid Ceres; Mineralogy
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2016.07.002

•Brucite–clay–carbonate mixtures are studied using VIS-IR reflectance spectroscopy.•Band parameters computed and correlations vs. endmember proportions retrieved.•Comparing with Ceres spectrum rules out presence of great amounts of brucite. Carbonates and clay minerals are present in Solar System bodies such as Mars and asteroid (1) Ceres. Brucite has been proposed in the recent past to fit absorption features in spectra of Ceres. In this study Visible-Near Infrared reflectance spectroscopic measurements have been performed on brucite–carbonate–clay minerals mixtures, in the 0.2–5.1µm spectral range. Different sets of three- and two-components mixtures have been prepared using these three fine powdered endmembers, by varying the relative proportions of carbonate, clay and brucite. Spectra have been acquired on the endmembers components separately and on the mixtures. Absorption features diagnostic of the carbonate, clay and brucite phases have been analyzed and band parameters (position, depth, area, width) determined. Several trends and correlations with mineral phase content in each mixture have been investigated, with the aim to determining how endmember components influence the mixture spectra and their minimum detectability threshold. Our results indicate that brucite is detectable in mineral mixtures with carbonates and clays, based on its main absorption features at 0.95, 2.45–2.47 and 3.05µm. While the 0.95 and 3.05 µm features are only discernible for very high brucite contents in the mixtures, the ∼2.45 µm band turns out to be highly diagnostic, also for very small amounts of brucite (of the order of 10wt%). These experiments, together with DAWN observations of Ceres, substantially rule out the presence of great amounts of brucite globally distributed on the surface of Ceres.