Experimental CO2 incorporation into Mg-cordierite: nonlinear behaviour of the system
Le Breton, Nicole; Schreyer, Werner
European Journal of Mineralogy Volume 5 Number 3 (1993), p. 427 - 438
published: Jun 14, 1993
manuscript accepted: Feb 18, 1993
manuscript received: Mar 31, 1992
ArtNo. ESP147050503013, Price: 29.00 €
Abstract High-pressure experiments were conducted to introduce CO2 molecules into the structural channels of a largely Al,Si-ordered Mg-cordierite. The run products were investigated by means of X-ray diffraction and infrared spectroscopy, and they were analysed for CO2 using a coulometric method. The cell parameter co of Mg-cordierite, which increases linearly with the CO2 content of the mineral, is suitable to characterize C02-bearing cordierites, whereas the cell parameter a0 and the distortion index Δ are too sensitive to the Al,Si-ordering state of cordierite to be used for this purpose. It was found that for any investigated P-T-t condition the cordierite CO2 content increases with the initial total CO2 content of the capsule. Moreover, for a fixed P-T condition and a specific total CO2 content in the capsule, the CO2 occupancy of cordierite channels oscillates as a function of time without reaching the saturation equilibrium. These unexpected phenomena are tentatively explained by a conflict between two processes: the stabilizing one is the diffusion of CO2 molecules into the channels, a tendency which would weaken with decreasing amount of CO2 gas in the capsule, and the destabilizing one is under discussion. The available experimental results clearly show the nonlinearity of the system. It is however possible that the "chaotic" behaviour of cordierite described in this paper does not occur in rocks because of the more gradual changes of CO2 contents in natural conditions.