Chemical Weathering of Iron 1) aA common example is the oxidation of iron. An iron atom that has given up two electrons forms a ferrous ion(Fe2+). When a ferrous ion is oxidized further by giving up a third electron, the result is a ferric ion(Fe3+) The incorporation of water in a mineral structure is called hydration The ferric hydroxide will soon dehydrate meaning it will lose some water, in which case it will form goethite(Feo.OH)
Chemical Weathering of Iron (1) ◼ A common example is the oxidation of iron. ◼ An iron atom that has given up two electrons forms a ferrous ion (Fe2+). ◼ When a ferrous ion is oxidized further by giving up a third electron, the result is a ferric ion (Fe3+). ◼ The incorporation of water in a mineral structure is called hydration. ◼ The ferric hydroxide will soon dehydrate, meaning it will lose some water, in which case it will form goethite (FeO.OH)
Chemical Weathering of Iron(2) Goethite may dehydrate still further to form hematite(Fe2 O3). The intensity of the colors of ferric hydroxide, goethite, and hematite ranging from yellowish through brownish red to brick red, can provide clues to how much time has elapsed since weathering began, and the degree or intensity of weathering
Chemical Weathering of Iron (2) ◼ Goethite may dehydrate still further to form hematite (Fe2O3). ◼ The intensity of the colors of ferric hydroxide, goethite, and hematite, ranging from yellowish through brownish red to brick red, can provide clues to how much time has elapsed since weathering began, and the degree or intensity of weathering
Combined Reactions ( 1) Almost all instances of chemical weathering involve more than one reaction pathway. Dissolution plays a part in virtually all chemical weathering processes and is usually accompanied by hydrolysis and leaching
Combined Reactions (1) ◼ Almost all instances of chemical weathering involve more than one reaction pathway. ◼ Dissolution plays a part in virtually all chemical weathering processes and is usually accompanied by hydrolysis and leaching
Combined Reactions (2) Calcite, if carbonic acid is present dissolves rapidly in rainwater. a The effects of these processes are widely seen in the distinctive landscapes- including caves, caverns, and sink- holes--underlain by carbonate rocks
Combined Reactions (2) ◼ Calcite, if carbonic acid is present, dissolves rapidly in rainwater. ◼ The effects of these processes are widely seen in the distinctive landscapes— including caves, caverns, and sinkholes—underlain by carbonate rocks
Effects of Chemical Weathering on Common Minerals and rocks(1) a When a granite decomposes, it does so by the combined effects of dissolution hydrolysis, and oxidation. Feldspar, mica, and ferromagnesian minerals weather to clay minerals and soluble Na+, K+, and Mgt ions. The quartz grains, being relatively inactive chemically, remain essentially unaltered
Effects of Chemical Weathering on Common Minerals and Rocks (1) ◼ When a granite decomposes, it does so by the combined effects of dissolution, hydrolysis, and oxidation. ◼ Feldspar, mica, and ferromagnesian minerals weather to clay minerals and soluble Na1+, K1+, and Mg2+ ions. ◼ The quartz grains, being relatively inactive chemically, remain essentially unaltered