Determination of the ratio hematite/goethite by soil color

Abstract

The content and composition of hematite and goethite can solve important tasks of genesis, as well as soil classification. It is proposed a new method of determining the index ILab = [Hematite/(Hematite+Goethite)] on color soil system CIE-L*a*b*. The method is based on calculating soils Redness (Red) and then calculating the ILab, based on reference Red of hematite and goethite. Replacement of Fe³⁺ to Al³⁺ is taken into account through amendments to the color of goethite, admitting that Al-hematite color does not differ from color pure hematite. The new technique was proven on Northern Italy andosols and was give results similar to results, received for conve-rting optical spectrum on Kubelka-Munk theory. But the new technique has the advantage of ease of calculation and the ability to use the old color data obtained in the Munsell system. Validating new methods in luvisols is showed an agreement index values ILab with real [Hematite/(Hematite+Goethite)] in those parts where there are profile have pure hematite and goethite. In luvisols containing Al-goethite and Al-hematite, admixture Al generates an error in the calculation. To delete the error, it is proposed an amendment to the distorting effects of aluminum in lattice goethite, with high content: 8-12 mole Al %. Cambisols have a value index ILab also vary depe-nding on the impurities Al in hematite and goethite. From samples with particles of pure goethite Red higher than cambisols conta-ining Al-goethite. After adjustment for the Al-share in goethite the share of hematite becomes comparable to its share in the cambisols samples with pure goethite.