Alternate Author Name(s)

Rosemary J. Vidale

Document Type


Date of Award



Clay minerals

Degree Name

Doctor of Philosophy (PhD)


Geological Sciences

First Advisor

Herman E. Roberson

Second Advisor

Marc W. Bodine


Clay minerals and feldspar were reacted with distilled water and natural and artificial sea water at 90° and 200°C for up to sir weeks and at 3500 C for three days. The data show that silica is released by clay minerals as a result of the dissolution of a disturbed surface layer. The amount of silica released by the clay minerals is dependent upon the temperature, the solution composition T (distilled vs. saline) and the solid:solution ratio.

Upon immersing clay minerals in artificial sea water to which silica had been added and heating to 90° C, either silica dissolution or sorption by the clays occurred as a function of the initial silica concentration. In distilled water, no sorption of silica occurred even at high initial silica concentrations, and at 200° C, no silica sorption was noted in either distilled water or artificial sea water.

The rate of transformation of montmorillonite to illite increases with increasing potassium concentrations and temperature. The reaction rate increased sharply between potassium concentrations of 1,250 and 2,500 ppm at 200° C. At 350° C, the reaction rate appeared to be much more uniform than at 200° C.

The transformation of montmorillonite to a less expandable phase was greatly retarded in solutions having a low K/Ca, Mg or Na ratio. Magnesium and calcium rich solutions were more effective in retarding the reaction rate than sodium rich solutions. The size of the ratio required to be effective in retarding the reaction is related to absolute potassium concentration and the temperature.

The rate of transformation of montmorillonite to a mixed—layer illite/montmorillonite phase during burial diagenesis, is believed to be dominantly controlled by the K/Cation ratio. The surficial release of silica by clay minerals and the silica released during the transformation of expandable clays to a less expandable phase, may be important in the silica cementation of shales and sandstones.