The parent material is the geological horizon from which soil horizons form; it is a key factor that in many cases determines the kinds and contents of secondary minerals of soils (Arbestain et al. 1999). Soils that develop from granite are likely to be more acidic than soils developed from calcareous limestone. In tropical and subtropical areas, under rainfall and high temperatures throughout the year, the process of acidification occurs over a long or a short time with the weathering of the soil parent material that liberates significant amounts of silica, iron, and aluminum and subsequent association of minerals of low crystallinity and aluminum-humus complexes (Garcia-Rodeja et al. 1987). In the humid tropics, most silicate minerals in the parent material are weathered away by desilication, leaving little other than the oxides of iron and aluminum (Sumner and Noble 2003).