Potential of vis-NIR reflectance spectroscopy for the mineralogical characterization of synthetic gleys: a preliminary investigation.

An investigation was carried out aiming at assessing the potential of vis-NIR reflectancespectroscopy, through comparison with the conventional X-ray powder diffraction (XRPD)technique, for the characterization of synthetic gleys, obtained in laboratory starting from Fe0and Fe2+ under different conditions of initial pH (5.5, 7.0 and 8.5). XRPD analysis showed thatin any case goethite formed, whereas magnetite and lepidocrocite developed in the lessoxidised, and akaganéite and hematite in the more oxidised environments. Magnetite was foundonly starting from Fe0, i.e. in the less oxidative condition, whereas sporadic hematite wasdetected just in Fe2+ synthetic gleys at 8.5 pH. Vis-NIR reflectance spectroscopy fullyconfirmed XRPD results. The features of reflectance spectra allowed (i) to discriminate Fe2+from Fe0 synthetic gleys; (ii) to detect goethite and akaganéite in the high-reflectance spectraof Fe2+ synthetic gleys; (iii) to correlate the very poor reflectance of Fe0 synthetic gley spectrato magnetite; and, (iv) to identify some goethite and lepidocrocite features in Fe0 syntheticgleys spectra. The analysis of second-derivative spectra also addressed to goethite, lepidocrociteand magnetite in Fe0 synthetic gleys; and (ii) goethite, akaganéite and - at pH 8.5 - hematite inFe2+ synthetic gleys. The results obtained appear to be as original as significant, introducingvis-NIR reflectance spectroscopy as an innovative and promising effective method for thecharacterization of the soil gley forms, and highly stimulating for further investigations.