Distribution of Ca and Na Ions in Dioctahedral Smectites and Interstratified Dioctahedral Mica/Smectites

Takashi Iwasaki1 and Takashi Watanabe2
Department of Geology, Faculty of Science, Kyushu University Hakozaki, Fukuoka, 812 Japan
1 Present address: Government Industrial Research Institute, Tohoku, Nigatake 4-2-1, Sendai, 983 Japan.
2 Present address: Joetsu University of Education, Yamayashiki 1, Joetsu, 943 Japan.

Abstract: The structures of 11 smectites and 2 interstratified mica/smectites containing mainly Ca2+ and Na+ as exchangeable cations in variable ratio were studied under a relative humidity of about 40%. Observed X-ray powder diffraction patterns were compared with diagrams calculated from interstratification models containing 15.2-Å Ca-smectite layers (C), 12.4-Å Na-smectite layers (N), and 10.0-Å mica layers (M) in various combinations. The smectites appear to be a random interstratification of component layers C and N, and display a tendency towards segregation. One of the interstratified minerals studied is a regular interstratification of C and M layers; the other is a regular interstratification of C, N, and M layers, in which N and C layers are randomly distributed in equal proportion and show a tendency towards segregation.

Key Words: Demixing • Exchangeable cations • Interstratified mica/smectite • Relative humidity • Smectite • Water • X-ray powder diffraction

Clays and Clay Minerals; February 1988 v. 36; no. 1; p. 73-82; DOI: 10.1346/CCMN.1988.0360110
© 1988, The Clay Minerals Society
Clay Minerals Society (www.clays.org)