Stability Relationships in Kaolinite, Gibbsite, and Al-hydroxyinterlayered Vermiculite Soil Systems1
- A. D. Karathanasis,
- Fred Adams and
- B. F. Hajek2
The stability of common soil minerals found in Ultisols was studied relative to their natural soil solution composition. The mineralogy of the clay fraction (<2 µm) ranged from 22 to 60% in kaolinite, 0 to 20% in gibbsite, 17 to 57% in hydroxyinterlayered vermiculite (HIV), and 1 to 12% in quartz. Ion activity functions (pH-⅓pAl and pH4SiO4) of soil solutions plotted on a stability diagram along with solubility lines of soil kaolinite, gibbsite, and HIV with the formula K0.24Ca0.08(Si3.24Al0.76)(Al1.56Fe0.24Mg0.20)[Al1.45(OH)3.79]O10(OH)2 indicated all solutions to be supersaturated with respect to reference kaolinite. Only a few surface soils containing gibbsite had solutions oversaturated relative to gibbsite. Solubility products of HIV were very close to its estimated pk, indicating a near-equilibrium condition with this mineral, especially in eluviated and transitional subsoil horizons (E and EB). Although the HIV appeared to be metastable relative to reference kaolinite, the data indicated a possible equilibrium coexistence of the two minerals with an HIV stability field below or above that of soil kaolinite, depending on the degree of Al-hydroxyinterlayering.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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