Nontronites are the ferric members of dioctahedral smectites, most of which are structural counterparts of beidellite (Brindley, 1980). The existence of a cont inuous b e i d e l l i t e n o n t r o n i t e series was suggested on the basis of chemical analyses by Ross & Hendricks (1945). However, a nontronite with montmorillonitic structure has been described by KSster (1982). Minor amounts of...