Reply to the Comment by Vidal, Dubacq, and Lanari on “The Role of H₃O⁺ in the Crystal Structure of Illite”

Abstract

The arguments of Vidal et al. (2010) against the incorporation of H₃O⁺ rather than of H₂O in the interlayer position of illite are disputable. Stoichiometric arguments do indeed suggest that the excess water in the Silver Hill illite is in the formof H₃O⁺. No reason exists to assume less water content in the IMt-2 sample than in those determined by Hower and Mowatt (1966) and confirmed by the thermogravimetric analyses of Nieto et al. (2010). The comparison between element contents calculated from end-members and those from the structural formula in figure 1 of Vidal et al. (2010) is not an experimental result, but rather a trivial mathematical artifact. The fact that thermodynamic models, based on the incorporation of interlayer H₂O in illite, may provide reasonable estimates neither proves nor disproves the presence of H₃O⁺; this is because thermodynamics is a non-atomistic, macroscopic approach.