Predict the possible reactions from the compositions of the phases in a system.

Unary system: C=1. All phases have same composition A “point”. Only phase transition is possible

Binary system: C=2. Phases are on a line.

3. Chemography

A B

1 2 3X

Example: Al2O3-H2O system Possible phases

Corundum Al2O3 (c)Diaspoer AlOOH (d)Gibbsite Al(OH)3 (g)Water H2O (w)

Al2O3 H2O

c wd g

When F=1, P + 1 = 2 + 2 =3. Thus, the following univariant reactions and

assemblages are possibled=c+gd=c+wg=d+wg=c+w

Ternary System: C=3, Phases are on a triangle

A

C

B

2

1

34

5

When F=1, P=3-1+2=4. Two possible univariant reactions;

Phase elimination reaction: 4=1+2+3 Join-crossing reaction: 1+2=3+4

A

C

B A

C

B

42

1

3

1

3

4

2

Example: SiO2-CaO-MgO-(H2O-CO2) system Possible phases

Quartz SiO2 (Qz) Calcite CaCO3 (Cc) Dolomite CaMg(CO3)2 (Dm) Tremolite Ca2Mg5Si8O22(OH)2 (Tr) Diopside CaMgSi2O6 (Dp) Forsterite Mg2SiO4 (Fo) Chondrodite Mg5Si2O8(OH)2 (Cd) Wollastonite CaSiO3 (Ws) Magnesite (MgCO3) (Mg)

With constant fugacities of H2O and CO2

CaO(C) MgO(M)

SiO2(S)

Cc

DmMg

Ws

Qz

Dp Tr

Fo

Cd

Metamorphic mineral reactions as a function of T

Qz+DmTr+Cc Qz+Tr+CcDpOriginal assemblage Cc+TrDi+Dm

Tr+Dm Di+Fo Di+Dm Cc+Fo