Thermodynamic data have been employed to construct theoretical solubility diagrams for quartz, kaolinite, and gibbsite at room temperature and pressure. Analysis of these diagrams indicates that gibbsite should not precipitate as a result of the dissolution of kaolinite unless quartz is absent from the system, the pH of the infiltrating water attains a value of at least 4.2, and the initial concentration of total dissolved silica in the infiltrating water is less than 10-4.6 moles per liter. These conclusions help explain why bauxites do not readily form on quartz rich rocks or in cooler regions where the pH of soil waters is commonly low because of the slow decay of organic matter.

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