Crystal Chemistry of Corrensite: A Review

Maria Franca Brigatti1 and Luciano Poppi2
1 Istituto di Mineralogia e Petrologia dell'Università, via S. Eufemia 19, 41100 Modena, Italy
2 Istituto di Mineralogia e Petrografia dell'Università, Porta S. Donato 1, 40100 Bologna, Italy

Abstract: Statistical analyses of chemical data from the literature of corrensite minerals suggest a large compositional variability, more evident in octahedral than in tetrahedral coordination. Mg occupies 40–80% of the octahedral sites, with Al and Fe2+ making up the remainder. Approximately 15–30% of the tetrahedral sites are filled by Al. Despite this compositional variability, distinct fields for the several types of mixed-layer trioctahedral chlorite/trioctahedral swelling layer are not apparent. Statistical analyses of the composition of corrensite compared with saponite, vermiculite, and chlorite suggest that corrensite is an intermediate between trioctahedral chlorite and trioctahedral smectite. If Fe/(Fe + Mg) > 50%, chlorite alone is favored, but with increasing Mg, chlorite appears to transform into corrensite and then, by iron oxidation, into trioctahedral smectite. Despite the chemical variability between corrensite, chlorite, and saponite, corrensite appears chemically to be a well-defined species. On the other hand, corrensite cannot be characterized chemically on the basis of its swelling component. Thus, the current definition of corrensite as a regular 1:1 interstratification of trioctahedral chlorite and either trioctahedral smectite or vermiculite is appropriate.

Key Words: Chemical composition • Corrensite • Mixed layer • Smectite • Statistical analysis • Vermiculite

Clays and Clay Minerals; October 1984 v. 32; no. 5; p. 391-399; DOI: 10.1346/CCMN.1984.0320507
© 1984, The Clay Minerals Society
Clay Minerals Society (www.clays.org)