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.
