Characterization of grumusols in southwestern Rio Grande do Sul. II. Mineralogical and genesis

Abstract

Quantitative mineralogical analyses were made on the soil and clay fractions of each of the map units, Bagé and Aceguá according to the mineralogical analyses as outlined by Alexiades and Jackson (1966) and by X-Ray diffraction. The analyses confirmed that montmorillonite is the predominant clay mineral. In addition, large quantities of primary minerals (feldspars, quartz and micas) occur that are in the process of being weathered with different intersites in diverse horizons and soils. The transformations proceed following the common sequences of weathering (Jackson 1964) with formation of 2:1 type clays and parte of these envolving into clays in a more advanced state of weathering. The Bagé soil is mineralogically and morphologically more developed, occuring in a more stable landscape. The genesis of both soils is closely related to the landscape form, climatic conditions and to the mineralogy of the parent material.