Hydrothermal Synthesis of Corrensite: A Study of the Transformation of Saponite to Corrensite

Herman E. Roberson1, R. C. Reynolds Jr.2 and David M. Jenkins1
1 Department of Geological Sciences, State University of New York at Binghamton, New York 13902
2 Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755

Abstract: Hydrothermal synthesis experiments were conducted to study the transition from smectite to corrensite. A mixture of oxides with the bulk composition of corrensite—Na0.4(Si6.4Al1.6)(Mg7..8Al1.2)-O20(OH)10—was sealed in platinum capsules with 29–37 wt. % water. One set of samples was treated in cold-seal vessels at 500°C and 2 kbar for durations of 2, 3, 6, 12, and 24 h; the other set was treated at 350°C and 2 kbar for periods of 12 to 89 d. X-ray diffraction patterns (XRD) of oriented aggregates from treated products were obtained from ethylene glycol-solvated and air-dried preparations. Samples were also heated to 350°C either in a calibrated muffle furnace, removed and quickly placed in a nitrogen filled chamber on the diffractometer, or were heated at 350°C by using a calibrated heating stage mounted on the diffractometer.

Initial mineral assemblages at both temperatures contained only saponite and serpentine. In experiments at 500°C, saponite transformed to corrensite within 6 h; in experiments at 350°C, the transformation occurred as early as 22 d. Increased experiment times at both temperatures produced increasing amounts of well-crystallized corrensite, as indicated by several well-defined XRD peaks. No evidence of a randomly interstratified chlorite-smectite (C-S) precursor to corrensite was found. The identification of pure smectite, as opposed to highly-expanded randomly interstratified C-S, was possible only when clays were dehydrated on a heating stage on the diffractometer.

These results call for a new examination of hydrothermally-altered basalt that has been reported to contain randomly interstratified C-S as an intermediate step in the reaction of smectite to corrensite or chlorite. These results also strengthen the view held by increasing numbers of investigators that corrensite should be regarded as a single phase, not as a mixed-layered phyllosilicate.

Key Words: Chlorite • Corrensite • Hydrothermal Synthesis • Randomly Interstratified Chlorite-Smectite • Saponite • X-ray Diffraction

Clays and Clay Minerals; April 1999 v. 47; no. 2; p. 212-218; DOI: 10.1346/CCMN.1999.0470211
© 1999, The Clay Minerals Society
Clay Minerals Society (www.clays.org)