Structure of fougerite and green rusts and a thermodynamic model for their stabilities

Fougerite is a new iron oxide, a mixed M(II)-M(III) hydroxide, a member of the green rust group. Its structure consists of a brucitic layer of Fe(III)-Fe(II)-Mg(II), where the excess of the positive charge due to Fe3+ is compensated in the interlayer by anions. The limits of composition are structurally and geochemically constrained, and the stabilities of the mineral and green rusts are obtained by a thermodynamic model of a regular solid solution, for different compensating anions and for any allowed composition of the brucitic layer. (c) 2005 Elsevier B.V. All rights reserved.