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In metamorphic geology, a compatibility diagram shows how the mineral assemblage of a metamorphic rock in thermodynamic equilibrium varies with composition at a fixed temperature and pressure. Compatibility diagrams provide an excellent way to analyze how variations in the rock's composition affect the mineral paragenesis that develops in a ...
This is the so-called metastable extensions rule: [1] The metastable extension of the [phase-absent] reaction must fall in the sector in which that phase is stable in all possible assemblages. A generic phase diagram with unspecified axes; the invariant point is marked in red, metastable extensions labeled in blue, relevant reactions noted on ...
A petrogenetic grid is a geologic phase diagram that plots experimentally derived metamorphic reactions at their pressure and temperature conditions for a given rock composition. This allows metamorphic petrologists to determine the pressure and temperature conditions under which rocks metamorphose.
In thermodynamics, the phase rule is a general principle governing multi-component, multi-phase systems in thermodynamic equilibrium.For a system without chemical reactions, it relates the number of freely varying intensive properties (F) to the number of components (C), the number of phases (P), and number of ways of performing work on the system (N): [1] [2] [3]: 123–125
Eskola's p,T-classification of metamorphic rocks founded modern metamorphic petrology, and the phase rule founds it. (That the Earth's crustal rocks are now visible because they are in metastable equilibrium was observed by Goldschmidt, and preceded these theorems.)
In petrology, metamorphic phases can be distinguished by analysis of minerals and microstructures (petrography) in metamorphic rocks.By analysing the sequence in which the minerals and structures were formed, more than one phase can be found in most metamorphic rocks (this is called polymetamorphism).
A miscibility gap between isostructural phases may be described as the solvus, a term also used to describe the boundary on a phase diagram between a miscibility gap and other phases. [2] Thermodynamically, miscibility gaps indicate a maximum (e.g. of Gibbs energy) in the composition range. [3] [4]
It is a special case of the Gibbs' phase rule for phases in thermodynamic equilibrium with each other, which states that C − P = F − 2 , {\displaystyle C-P=F-2,} where C is the minimum number of chemical components , P is the number of phases , and F is the number of degrees of freedom (e.g., temperature and pressure) that can vary without ...