Experimental CO (sub 2) incorporation into Mg-cordierite; nonlinear behaviour of the system

High-P experiments to introduce CO (sub 2) molecules into the structural channels of a largely Al,Si-ordered synthetic Mg- cordierite are reported. The products were examined by XRD and analysed for CO (sub 2) using a coulometric method. The c cell parameter of Mg-cordierite increases linearly with the CO (sub 2) content and is suitable for characterizing CO (sub 2) -bearing cordierites, whereas the a parameter and the distortion index DELTA are too sensitive to the Al,Si-ordering state of cordierite to be used for this purpose. For any P-T-t condition the cordierite CO (sub 2) content increases with the initial CO (sub 2) content of the capsule; for a fixed P-T condition and a specific total CO (sub 2) content in the capsule the CO (sub 2) occupancy of the channels oscillates as a function of time without reaching equilibrium. It is, however, possible that this behaviour of cordierite does not occur in rocks because of the more gradual changes of CO (sub 2) contents in natural conditions.