eventually be forming on. Rock types that form the base of the soil profile are often either sedimentary (carbonate or siliceous), igneous or metaigneous (metamorphosed igneous rocks) or volcanic and metavolcanic rocks. The rock type and the processes that lead to its exposure at the surface are controlled by the regional geologic setting of the specific area under study, which revolve around the underlying theory of plate tectonics, subsequent deformation, uplift, subsidence and deposition. Metaigneous and metavolcanic rocks form the largest component of cratons and are high in silica. Igneous and volcanic rocks are also high in silica but with non-metamorphosed rock, weathering becomes faster and the mobilization of ions is more widespread. Rocks high in silica produce silicic acid as a weathering product. There are few rock types that lead to localized enrichment of some of the biologically limiting elements like phosphorus (P) and nitrogen (N). Phosphatic shale (< 15% P2O5) and phosphorite (> 15% P2O5) form in anoxic deep water basins that preserve organic material. Greenstone (metabasalt), phyllite and schist release up to 30–50% of the nitrogen pool. Thick successions of carbonate rocks are often deposited on craton margins during sea level rise. The widespread dissolution of carbonate and evaporate minerals leads to elevated levels of Mg2+, , Sr2+, Na+, Cl− and ions in aqueous solution. Weathering and dissolution of minerals The process of soil formation is dominated by chemical weathering of silicate minerals, aided by acidic products of pioneering plants and organisms as well as carbonic acid inputs from the atmosphere. Carbonic acid is produced in the atmosphere and soil layers through the carbonation reaction. H2O + CO2 <=> H+ + HCO3- H2CO3 This is the dominant form of chemical weathering and aides in the breakdown of carbonate minerals such as calcite and dolomite and silicate minerals such as feldspar. The breakdown of the Na-feldspar, albite, by carbonic acid to form kaolinite clay is as follows: 2 NaAlSi3O8 + 2 H2CO3 + 9 H2O <=> 2 Na+ + 2 HCO3- + 4 H4SiO4 + Al2Si2O5(OH)4 Evidence of this reaction in the field would be elevated levels of bicarbonate (), sodium and silica ions in the water runoff. The breakdown of carbonate minerals: CaCO3 + H2CO3 <=> Ca^2+ + 2 HCO3- CaCO3 <=> Ca^2+ + CO3^2- The further dissolution of carbonic acid (H2CO3) and bicarbonate () produces CO2 gas. Oxidization is also a major contributor to the breakdown