A new thermodynamic model for clino- and orthoamphiboles in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2 -H2O-O

Abstract

A recent thermodynamic model for the Na-Ca clinoamphiboles in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2 -H2O-O (NCFMASHO), is improved, and extended to include cummingtonite-grunerite and the orthoamphiboles, anthophyllite and gedrite. The clinoamphibole model in NCMASH is adopted, but the extension into the FeO- and Fe2O3-bearing systems is revised to provide thermodynamic consistency and better agreement with natural assemblage data. The new model involves order-disorder of Fe-Mg between the M2, M13 and M4 sites in the amphibole structure, calibrated using the experimental data on site distributions in cummingtonite-grunerite. In the independent set of end-members used to represent the thermo..