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Water is the principal agent of chemical weathering, converting many primary minerals to clay minerals or hydrated oxides via reactions collectively described as hydrolysis. Oxygen is also important, acting to oxidize many minerals, as is carbon dioxide, whose weathering reactions are described as carbonation. [22]
Some mineral structures, for example, montmorillonite, are capable of including a variable amount of water without significant change to the mineral structure. [citation needed] Hydration is the mechanism by which hydraulic binders such as Portland cement develop strength. A hydraulic binder is a material that can set and harden submerged in ...
Hydrolysis (/ h aɪ ˈ d r ɒ l ɪ s ɪ s /; from Ancient Greek hydro- 'water' and lysis 'to unbind') is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution , elimination , and solvation reactions in which water is the nucleophile .
Mineral alteration refers to the various natural processes that alter a mineral's chemical composition or crystallography. [1]Mineral alteration is essentially governed by the laws of thermodynamics related to energy conservation, relevant to environmental conditions, often in presence of catalysts, the most common and influential being water (H 2 O).
Hydrolysis is a chemical weathering process affecting silicate and carbonate minerals. In such reactions, pure water ionizes slightly and reacts with silicate minerals. An example reaction: Mg2SiO4 + 4H+ + 4OH- ⇌ 2Mg2+ + 4OH- + H4SiO4 olivine (forsterite) + four ionized water molecules ⇌ ions in solution + silicic acid in solution
Chemical weathering of feldspars happens by hydrolysis and produces clay minerals, including illite, smectite, and kaolinite. Hydrolysis of feldspars begins with the feldspar dissolving in water, which happens best in acidic or basic solutions and less well in neutral ones. [30]
For example, calcium silicate (CaSiO 3), or wollastonite, reacts with carbon dioxide and water to yield a calcium ion, Ca 2+, a bicarbonate ion, HCO 3 −, and dissolved silica. This reaction structure is representative of general silicate weathering of calcium silicate minerals. [9] The chemical pathway is as follows:
Under the unusual chemical conditions accompanying serpentinization, water is the oxidizing agent, and is itself reduced to hydrogen, H 2. This leads to further reactions that produce rare iron group native element minerals, such as awaruite (Ni 3 Fe) and native iron; methane and other hydrocarbon compounds; and hydrogen sulfide. [1] [6]