DISTRIBUTION OF Ca AND Na IONS IN DIOCTAHEDRAL SMECTITES AND INTERSTRATIFIED DIOCTAHEDRAL MICA/SMECTITES

Abstract- The structures of 11 smectites and 2 interstratified mica/smectites containing mainly Ca 2. 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 interstratifi-cation models containing 15.2- ~ Ca-smectite layers (C), 12.4-/k Na-smectite layers (N), and 10.0- ~ mica layers (M) in various combinations. The smectites appear to be a random interstratification f component layers C and N, and display a tendency towards egregation. One of the interstratified minerals tudied is a regular interstratification f C and M layers; the other is a regular interstratification f C, N, and M layers, in which N and C layers are randomly distributed inequal proportion and show a tendency towards segregation. Key Words--Demixing, Exchangeable cations, Interstratified mica/smectite, Relative humidity, Smectite, Water, X-ray powder diffraction