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3. Chemography

3. Chemography. 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. 1. 2. 3. X. A. B. Example: Al2O3-H2O system

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3. Chemography

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  1. 3. Chemography • 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 • Binarysystem: C=2. Phases are on a line. 1 2 3 X A B

  2. Example: Al2O3-H2O system • Possible phases • Corundum Al2O3 (c) • DiaspoerAlOOH (d) • Gibbsite Al(OH)3 (g) • Water H2O (w) c d w g Al2O3 H2O

  3. When F=1, P + 1 = 2 + 2 =3. • Thus, the following univariant reactions and assemblages are possible • d=c+g • d=c+w • g=d+w • g=c+w

  4. Ternary System: C=3, Phases are on a triangle C 1 2 3 4 5 A B

  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 C C 1 1 4 4 2 3 3 2 B B A A

  6. 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

  7. SiO2(S) Qz Tr Dp Ws Fo Cd Cc Mg Dm CaO(C) MgO(M)

  8. Metamorphic mineral reactions as a function of T Original assemblage Qz+DmTr+Cc Qz+Tr+CcDp Cc+TrDi+Dm Tr+DmDi+Fo Di+DmCc+Fo

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