Implication from the examination of spectral library of hydroxylated and/or hydrated silicate minerals at 1.0–2.5 um wavelengths

Hyperspectral imaging is broadly used in the identification of hydroxylated and hydrated silicate minerals, especially at the wavelengths of 1.0-2.50 μm. The vibrations of the hydroxyl (OH) molecule, water molecule (H-O-H), and metal-OH bonds, or their combinations, produce prominent absorption features at ~1.40, ~1.91 and 2.20-2.40 μm wavelengths. In remote sensing applications minerals showing one or two of these absorption features are usually categorized as hydroxylated and/or hydrated, and minerals showing all three absorption features are usually categorized as hydrated phyllosilicates. In this paper we examined the spectral library of common silicate minerals and found that some showing these absorption features are not hydroxylated and/or hydrated but with tiny alteration or impurities. This implies that the identification of hydroxylated and/or hydrated silicate minerals can´t be merely based on these absorption features and the incorporation of geology and environment in situ is very important. We also calculated absorption depths and silicate mineral ratios in these absorption features as references for discrimination. This study provides a cautionary perspective on the identification of hydrated phyllosilicate minerals with respect to mineralogical interpretations of Mars and other planets.