Crystal Growth Mineral Formation & Stability Gibbs Free Energy ...

• Phase = physically separable portion of the system that is
chemically and physically distinct from everything else in
the system (e.g. one phase is present when sugar & milk is
dissolved in the coffee, but two phases exist when the
sugar is sitting on the bottom of the cup instead of
dissolved in the coffee)
• Components = each phase is composed of 1+ components;
chosen by scientist, but you try to choose as few
components as possible that describe your entire system
http://www.tulane.edu/~sanelson/eens211/mineral_stability.htm
1
3
http://csmres.jmu.edu/geollab/Fichter/IgnRx/BinryEu.html
2
A
B
AB
BC
BCA
E. Goeke, Fall 2006
E. Goeke, Fall 2006
E. Goeke, Fall 2006
Phase Rule
• Phase rule = used to determine how many variables &
equations are required to describe a system that’s in
equilibrium
• Variables:
– Number of chemical components
– Extensive variables (pressure & temperature)
• F = C + 2 - P
– F = degrees of freedom or variance of the system
– C = number of components (as defined on the last slide)
– P = number of phases in equilibrium
– 2 comes from P & T
2 Component Eutectic Systems
http://csmres.jmu.edu/geollab/Fichter/IgnRx/BinryEu.html
http://csmres.jmu.edu/geollab/Fichter/IgnRx/BinryEu.html
E. Goeke, Fall 2006
• Liquidus = line
that separates all
melt and melt +
xtal
• Solidus = line that
separates melt +
xtal and all xtal
• Eutectic = point at
which melt + A +
B exists
E. Goeke, Fall 2006
E. Goeke, Fall 2006
E. Goeke, Fall 2006, 12:041 Mineralogy 2