Mineralogy and behavior of tropical soils

While they are not typical of all tropical soils, the large majority of such soils have similar features. A fundamental property of a soil mineral is the sign and magnitude of the charge on its surface. Minerals in tropical soils which behave as variable charge colloids are the crystalline and non-crystalline oxides and hydrous oxides of silicon, aluminum, iron, manganese and titanium. Non-crystalline alumino-silicates also behave as variable charge colloids. In soils with variable charge minerals, specific absorption of anions causes the cation exchange capacity to decrease. For these soils, prediction of soil behavior will be improved if a model based on variable charge colloid is used.