Phase Rule and Phase Diagrams | One Component System | Igneous Petrology | Geology | GATE | NET, JAM

#Geology #Petrology #IgneousPetrology #GATE #IITJAM #CSIRNET #earthscience #PhaseRule #Geomind
Phase Diagrams and Phase rule.
Why Study them ?
• Rocks are made of an assemblage of minerals they melt over a range of temperature.
• Rocks melt at much lower temperatures than do any of their constituent minerals
• The melting processes are shown graphically in phase diagrams, which show the composition of minerals that coexist with liquids in terms of temperature (also pressure).
• Phase diagrams are important to understanding igneous rocks
and interpreting their textures.
• behavior of materials in Earth systems can be modeled using thermodynamic calculations and/or laboratory investigations. The
results of such calculations and/or investigations are commonly summarized on phase stability diagrams
• Phase stability diagrams display the stability fields for various
phases separated by lines representing conditions under which phase changes occur
phase diagrams are graphical representations of the equilibrium relationships between minerals (or others phases). These relationships are governed by the laws of thermodynamics. Standard phase diagrams show how phases or phase assemblages change as a function of temperature, pressure, phase composition, or combinations of these variables
Pseudo-sections are a type of phase diagram that shows the fields of stability of different equilibrium mineral assemblages for a single bulk-rock composition.
P+F= C+2-r or P+F=C+2 (Gibbs Phase Rule)
A phase is defined as a type of physically distinct homogenous material
in a system that is mechanically separable from the rest. A phase may be a mineral, a liquid, a gas, or an amorphous solid such as glass. A piece of ice is a single phase, whereas ice water consists of two phases (the ice and the
water are separable).

E.g.- Minerals in rocks are solid crystalline phases (Olivine and Plagioclase) are two phases in basalt.
#A component is a chemical constituent, such as Si, H2O, O2, SiO2, or NaAlSi3O8.
#The components can be defined as the minimum number of chemical species required to completely define the system and all of its phases
• A pure mineral, such as albite, has a single component (NaAlSi3O8).
• Minerals that exhibit solid solution, however, are commonly treated as multicomponent systems.
• Plagioclase is commonly a single phase that comprises two components: NaAlSi3O8 and CaAl2Si2O8.
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