the reducible material of a soil maimly composed of iron and manganess oxides, in particular know to fix the metals in trace amounts. such as clays, metal oxyhydroxides are secondary minerals resulting fromweathering processes, slightly soluble in the pH rang of soils. tthey are divided into three size classes; in the form of "coatings" , "bridges" between the various components of the soil or "concretions" as isolated particles