A Contribution to the Study of the Stability of Clay Minerals from the Soil Solution Composition at Different pF Values

M. L. Fernandez-Marcos, F. Macías and F. Guitián-Ojea
Cátedra de Edafología, Facultad de Farmacia, Santiago de Compostela, Spain

Abstract: The composition of the soil solution of various horizons of Galician soils was studied to gain insight into the direction of the processes of weathering and neoformation by means of stability diagrams of the clay minerals. The soil solution was extracted by compression at various pF values.

The most significant results are as follows. In all the cases studied the mineral in equilibrium with the soil solution is a 1:1 philosilicate. As the pF at which the soil solution is extracted increases, corresponding to smaller pore size, pH increases and silica concentration falls. The stable mineral does not vary significantly between different horizons of the same profile. Each parent material gives rise to a different zonation in the stability diagrams. The predictions of the stability diagrams are in general agreement with the mineralogical data of the clays of the horizons in question.

Finally, weathering processes in Galicia are briefly commented on.

Clay Minerals; March 1979 v. 14; no. 1; p. 29-37; DOI: 10.1180/claymin.1979.014.1.04
© 1979, The Mineralogical Society
Mineralogical Society (www.minersoc.org)