Ideal site-mixing applied to solutions involving coupled substitution
European Journal of Mineralogy Volume 6 Number 3 (1994), p. 355 - 364
published: Jun 7, 1994
manuscript accepted: Jan 12, 1994
manuscript received: Aug 23, 1993
ArtNo. ESP147050603002, Price: 29.00 €
Abstract The ideal site-mixing model is applied to binary two-site solutions (A,B)αm and (C,D)βn with chargecoupling between substitutions (A-1B)α and (C-1D)β assuming no local electrostatic charge-balance. The resulting activity-composition relations are systematized with respect to ideal mixing entropy, configurational entropy of the solution, and choice of components within the composition space AmCn-BmCn-AmDn-BmDn. Five types of activity-composition relations can be distinguished: a) ideal molecular type or transformable to such type, b) regular symmetric type, c) regular asymmetric type, d) asymmetric activities, of which one is non-Henrian and Raoultian, the other is non-Raoultian and Henrian, and e) activities for which a1≠0 when Xi = 0, transformable to one of the other types. The muscovite-celadonite and phlogopite-eastonite binaries are used as examples.