Review of the Relationships in the Montmorillonite Group of Clay Minerals

Abstract Since the publication of the paper on the minerals of the montmorillonite group by Ross and Hendricks (1945) some species have been added to the group, and minor changes in the acceptable species have become advisable. No radical changes are proposed, but a review of the members and their grouping will be presented. The acceptable dioctahedral members of the group appear to be montmorillonite, nontronite and volchonskoite. Beidellite should be discontinued. The acceptable trioetahedral members of the group appear to include saponite, hectorite, sauconite, stevensite and medmontite. Griffithite is probably a useful term for an iron-rich saponite. Representative chemical analyses and formulas have been assembled to illustrate relationships.