Water and Magmas: Clarification of a Controversy on Applications of the Gibbs-duhem Equation.
Geochem Cosmochim Acta 43:637-641
Contrary to the claims of others, it is shown mathematically that if the activity of water in ternary water-magma (aluminosilicate) systems is constant or varies only with the mole fraction of water, it is not necessary that the binary magmas form ideal solutions. A molecular viewpoint is presented to support this argument. The properties of analytical equations capable of representing the activity coefficients of usual and unusual systems are discussed. The correct form of the Gibbs-Duhem equation for dissociative dissolution processes is presented.
Geochem. Cosmochim. Acta, V. 43, PP. 637-641