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Scientia Agricola

On-line version ISSN 1678-992X


CLEMENTE, Celso Augusto; DEMATTE, José Alexandre Melo; MAFRA, Álvaro Luiz  and  BENTIVENHA, Sérgio Ricardo Portes. Spectral reflectance and mineralogy of soil materials developed from diabase. Sci. agric. [online]. 2000, vol.57, n.1, pp.159-168. ISSN 1678-992X.

The aim of this study was to characterize soil materials with different degrees of weathering and then associate their composition with their spectral behavior. One pedological profile developed from diabase was studied in Capivari-SP, Brazil. The morphological description allowed to separate six phases of rock-soil alteration. Afterwards, granulometry, chemical and mineralogical analysis were carried out. The soil spectral reflectance was evaluated with a laboratory spectroradiometer using the wavelength range of 300 to 2500 nm. The profile was moderately weathered as evidenced by a high silt/clay ratio, found below the Bi horizon. Subsurface horizons also presented high nutrient status, especially for P, Ca and Mg, which was related to the occurence of saprolite with an abundance of easily weathered minerals. The mineral evolution began with the precipitation of iron oxides and 2:1 clay minerals, like vermiculite and vermiculite-smectite, and this led to the formation of kaolinite and gibbsite in the upper part of the soil profile. Spectral behavior generally was in conformity with their mineralogical composition, pointing out to the presence of iron oxides, various groups of clays and primary minerals, such as pyroxenes and magnetite.

Keywords : caolinite; spectral reflectance; gibbsite; basic rock; vermiculite-smectite.

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