Chemical Composition of the Geosphere and Geochemistry

FIGURE 9.4 Representation of the structure of kaolinite, a two-layer clay, in which layers of hydrated Si(lV) oxide alternate with layers of Al(III) oxide. 

Rainwater, which is free of alkalinity and hardness ions, but is somewhat acidic due to dissolved CO2 and sometimes other acidic constituents, such as those characteristic of acid rain (see Section 4.8), is an aggressive weathering agent. 

There are several important processes in which water is involved in chemical weathering. Water acts as a solvent to dissolve minerals. 

CaS04 2H20(s)(water) Ca + (aq) + SO (aq) + 2H2O may add to minerals in hydration reactions, 

CaS04 (s) + 2H2O CaS04 2H20(s) or be lost in dehydration processes  

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