1. Hot Under the Collar (part III) Phase Diagrams
Rocks at last!!!!

2. Gibbs Phase Rule F = C - P + 2 F = the number of degrees of freedom
C = the number of components
P = number of phases

3. Gibbs Phase Rule Divarient Field Point C F = C - P + 2 Only one phase
Only one component (e.g. H2O exists as ice, water and steam but is always present as H2O)
Therefore two degrees of freedom
Divarient Field

4. Gibbs Phase Rule Univarient Line Point B F = C - P + 2 Two phases
Only one component (e.g. H2O exists as ice, water and steam but is always present as H2O)
Therefore one degree of freedom
Univarient Line

5. Gibbs Phase Rule Invarient Point Point A F = C - P + 2 Three phases
Only one component (e.g. H2O exists as ice, water and steam but is always present as H2O)
Therefore no degrees of freedom
Invarient Point

6. Two component phase diagrams – mixtures between two endmembers
Binary Phase Diagrams
Two component phase diagrams – mixtures between two endmembers

7. Binary Phase Diagrams
Eutectic
Liquidus
Solidus

8. Equilibrium
BALANCE
MgO + SiO MgSiO3
periclase
quartz
enstatite

9. Binary Phase Diagrams

10. Binary Phase Diagrams

11. Binary Phase Diagrams

12. Binary Phase Diagrams

13. Lever Rule
F = L2/L1
F is the fraction of melt remaining

14. Lever Rule
F = L3/L1
F is the fraction of crystals of B L3

15. Lever Rule
F = L2/L1
F is the fraction of crystals of B generated at the eutectic

16. Lever Rule
F = L2/L1
F is the fraction total fraction of B in the whole rock

17. Disequilibrium Reactions are not balanced Rapid cooling
Separation of crystals by sinking or flotation (crystal differentiation)
“Protection” of crystals by the formation of rims or zoning.

18. At Disequilibrium

19. At Disequilibrium

20. At Disequilibrium

21. At Disequilibrium

22. Solid Solutions

23. Solid Solutions

24. Solid Solutions

25. Lever Rule
F = L2/L1
F is the fraction of liquid left.

26. Under Disequilibrium

27. Under Disequilibrium

28. Under Disequilibrium

29. Why phase diagrams are the way they are!!!!
Next Time
Why phase diagrams are the way they are!!!!