『Abstract
This paper presents a novel concept in the thermodynamic derivation
of phase diagrams for clay minerals that incorporates fuzzy transition
zones. This new technique yields phase diagrams that have graded
(fuzzy) zones of mineral occurrences and includes compositional
variability within mineral groups. For the construction of these
diagrams, 170 minerals belonging to nine different subgroups were
used, based on a fuzzy mathematical description of their ‘grades’
or ‘belonging-ness’. Standard free energies of formation of all
the minerals were derived and all possible pairs of mineral equilibria
were evaluated. Relative intensities of mineral occurrences were
determined and membership values of each type of mineral at various
zones in a 2D or 3D space were graphically represented. Computations
and graphical representations were carried out using programs
developed in Mathematica. Diagrams were derived for 25℃,
1 bar with a solution phase containing Si(OH)4,
K+, Na+, H+, Ca2+
and Mg2+ under conditions of gibbsite, goethite and
ferrous oxide saturation. The resulting diagrams, unlike conventional
phase diagrams, show multimineral assemblages, with varying occurrences
of different minerals and provide a realistic representation of
clay mineral occurrences formed by surface geochemical processes.
They show that on the Earth's surface, only montmorillonite can
almost completely predominate the inorganic phase followed by
kaolinite, illite and beidellite. Nontronite, glauconite, celadonite
and vermiculite would not be neoformed in substantial amounts.
A general conformity of derived phase equilibria with experimentally
observed equilibria is also observed.
Key Words: Equilibria; Free energy; Fuzzy; Illite; Kaolinite;
Montmorillonite; Phase; Program; 2D; 3D』
Introduction
Methodology
Results
Conclusions
Acknowledgments
References
Appendix