A MATHEMATICAL MODEL TO D IST INGUISH THE MEMBERS OF THE D IOCTAHEDRAL SMECTITE SERIES

A B ST R A C T: St atistical (Q-mode) analysis of the chemical compositions of 122 dioctahedral smectites obtained from the literature have enabled the main solid solution ranges (montmoril-lonite, beidellite and nontronite) to be distinguished on a triangular diagram. In the montmorillonite area, the Wyoming, Tatatilla, Otay, Chambers and Non-Ideal montmorillonite compositional ranges are identified. Certain crystallochemical features of the smectites may be correlated with different genetic environments. Many workers have attempted torationalize the compositional differences found in the dioctahedral smectites. Vogt & K6ster (1978), using a ternary diagram with vertices representing pyrophyllite, celadonite and muscovite, differentiated montmorillonite, nontronite and beidellite on the basis of crystallochemical features, although the area for montmorillonite was very restricted and other compositional ranges could not be characterized. Grim & Kulbicki (1961), using chemical and other data, showed that montmorillonite does not form a single continuous i omorphous series, and suggested that there were two different aluminous types (Cheto and Wyoming) which differed primarily in the population of their octahedral layers. Again, however, many members o