Compositions of gismondine, cymrite, anorthite, and celsian solid solutions

Resumo

This paper presents a three-dimensional geometric analysis of the homogeneity regions of gismondine, cymrite, anorthite, and celsian solid solutions with the use of two composition tetrahedra: AO–BO_0.5–AlO_1.5–SiO₂ and AO–AlO_1.5–SiO₂–H₂O (where A = alkaline-earth element and B = alkali element). The main general aspects of the extension of the homogeneity regions are elucidated. The position of the homogeneity regions in the composition tetrahedra suggests that increasing the percentage of SiO₂ should lead to a gismondine–cowlesite phase transition and that a few phase transitions should be expected in the course of gismondine dehydration, which will lead to the formation of a solid solution with the anorthite structure after all of the water will be removed.