GEOL 104 Lecture Notes - Lecture 15: Humus, Soil Chemistry, Soil Horizon
Weathering: involves the physical breakdown and chemical alteration of rock at or near earths surface, with no transportation. Mechanical weathering: physical forces breaking rocks into smaller pieces: increases surface area surface controlled processes as mechanical weathering breaks rock into smaller pieces, more surface area is exposed to chemical weathering. Chemical weathering: chemical transformation of rock into new compounds: dissolution: certain minerals dissolve in water. Halite is one of the most water-soluble minerals. Small amount of water increases the corrosive force of water, causing dissolution. Carbonic acid: created when carbon dioxide dissolves in raindrops. Calcite: easily attacked by weakly acidic solutions. Limestone disassociates under weather conditions: oxidation: oxygen combines with iron to form iron oxide. Water increases the speed of the reaction important in decomposing ferromagnesian. Minerals like olivine, pyroxene, hornblende, and biotite. Severe weathering of silicates in tropics produces bauxite. In humid tropical climates, clay minerals break down further, into aluminum oxides and hydroxides, referred to as bauxite.