Synthesis and Paragenesis of Na-Beidellite as a Function of Temperature, Water Pressure, and Sodium Activity*

J. Theo Kloprogge1, **, A. M. J. van der Eerden1, J. Ben H. Jansen1, ***, John W. Geus2 and Roelof D. Schuiling1
1 Institute of Earth Sciences, Department of Geochemistry, University of Utrecht, Budapestlaan 4, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands
2 Department of Inorganic Chemistry, University of Utrecht, P.O. Box 80.083, 3508 TB Utrecht, The Netherlands
* Publication of the Debye Institute, University of Utrecht.
** Present address: Plastics and Rubber Institute TNO, P.O. Box 108, 3700 AC Zeist, The Netherlands.
*** Present address: Bowagemi, Prinses Beatrixlaan 20, 3972 AN Driebergen, The Netherlands.

Abstract: In the chemical system Na2O-Al2O3-SiO2-H2O, the stability field of Na-beidellite is presented as a function of pressure, temperature, and Na- and Si-activity. Na0.7-beidellite was hydrothermally synthesized using a stoichiometric gel composition in the temperature range from 275° to 475°C and at pressures from 0.2 to 5 kbar. Below 275°C kaolinite was the only crystalline phase, and above about 500°C paragonite and quartz developed instead of beidellite. An optimum yield of 95% of the Na0.7- beidellite was obtained at 400°C and 1 kbar after 20 days. Gels with a Na-content equivalent to a layer charge lower than 0.3 per O20(OH)4 did not produce beidellite. They yielded kaolinite below 325°C and pyrophyllite above 325°C. With gels of a Na-content equivalent to a layer charge of 1.5, the Na-beidellite field shifted to a minimum between temperatures of 275° and 200°C. This procedure offers the potential to synthesize beidellite at low temperatures. Beidellite synthesized from Na1.0-gel approach a Na1.35 composition and those from Na1.5- and Na2.0-gels a Na1.8 composition.

Key Words: Beidellite • Electron microprobe • Hydrothermal synthesis • Kaolinite • Paragonite • Pyrophyllite • Scanning electron microscopy • X-ray diffraction

Clays and Clay Minerals; August 1993 v. 41; no. 4; p. 423-430; DOI: 10.1346/CCMN.1993.0410403
© 1993, The Clay Minerals Society
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