L08_Sedimentary_Rocks_Chemical_Weathering

5ca 05mg co3 h2o urey reacon simplied

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Unformatted text preview: source: Urey Reac<on: igneous rock rainfall atmosphere H2O + CO2 + CaSiO3 à༎ SiO2 + Ca++ + CO3- - + H2O Urey Reac<on, Simplified CaSiO3 + CO2 à༎ SiO2 + CaCO3 note: CaCO3 is calcite (aragonite), the primary cons<tuent of the abundant rocks limestone and marble. SiO2 is silica (or quartz), one of the most common minerals. What if Mg is an important ca<on? source: Urey Reac<on: igneous rock rainfall atmosphere H2O + CO2 + (Ca,Mg)SiO3 à༎ SiO2 + 0.5Ca++ + 0.5Mg++ + CO3- - + H2O Urey Reac<on, Simplified (Ca,Mg)SiO3 + CO2 à༎ SiO2 + (Ca,Mg)CO3 note: (Ca,Mg)CO3 is dolomite, another primary cons<tuent of carbonate rocks What about sodium (Na)? source: Urey Reac<on: igneous rock rainfall atmosphere H2O + CO2 + Na2SiO3 à༎ SiO2 + 2Na+ + CO3- - + H2O Urey Reac<on, Simplified Na2SiO3 + CO2 à༎ SiO2 + 2Na+ + CO3- - note: Sodium carbonate (Na2CO3) is soluble in water. Therefore weathering of Na- containing igneous rocks does not produce sedimentary carbonate rocks. Same goes for potassium (K). Ca, Mg are necessary for carbonate rock produc<on! Short- term Carbon cycle Long- term Carbon cycle How does CO2 func<on as an acid? dissolu<on of CO2 in water creates carbonic acid: H2O + CO2 à༎ H2CO3 carbonic acid naturally dissociates to create H+ (acid), and HCO3- (bicarbonate) H2CO3 à༎ H+ + HCO3- pure water in equilibrium with atmospheric CO2 has a pH of 5.6 rainfall is pure water and...
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