Mineral pairs to be considered

	Halloysite	Kaolinite	Muscovite	Microcline	Albite
Gibbsite	X	X	x	x	x
Halloysite		X	x	x	x
Kaolinite			x	x	x
Muscovite				x	x
Microcline					x

Recall, DG = -RT lnKeq

Simplifying assumptions: 1. solution always present; 2. Al always in solid phase; 3. Silica is fixed by quartz saturation; 4) P and T are constant at 1 bar and 25°C; and 5) Activities of solids and water are unity.

Kaolinite - Gibbsite

Al2Si2O5(OH)4 + 5H2O <-----> 2Al(OH)3 + 2H4SiO4^o

Keq = a2H4SiO4^o

log(Keq) = 2 loga H4SiO4^o = -10.4

loga H4SiO4^o = -5.20

(note: because the activity of dissolved silica at quartz saturation is greater than the activity of silica with kaolinite and gibbsite in equilbrium (i.e. -3.95 > -5.20) , the above reaction proceeds from right to left).

Quartz - Silica

SiO2 + 2H2O <-----> H4SiO4^o

Keq = aH4SiO4^o

log(Keq) = loga H4SiO4^o

loga H4SiO4^o = -3.95

Halloysite - Gibbsite

Al2Si2O5(OH)4 + 5H2O <-----> 2Al(OH)3 + 2H4SiO4^o

Keq = a²H4SiO4^o

log(Keq) = 2 loga H4SiO4^o = -7.11

loga H4SiO4^o = -3.56

(Note: because the activity of dissolved silica at quartz saturation is less than the activity of silica with halloysite and gibbsite in equilbrium (i.e. -3.95 < -3.56) , the above reaction proceeds from left to right. But furthur note, that all gibbsite goes to kaolinite from the kaolinite-gibbsite reaction above).

Microcline - Kaolinite

2KAlSi3O8+ 9H2O + 2H⁺ <-----> 2K⁺ + 4H4SiO4^o + Al2Si2O5(OH)4

Keq = (a²K⁺ a⁴H4SiO4^o) / (a²H+)

log(Keq) = 2 log (aK⁺ / aH⁺) + 4 loga H4SiO4^o = -3.96

log(aK⁺ / aH⁺)+ 2 loga H4SiO4^o = -1.98

Recall, that at quartz saturation, loga H4SiO4^o = -3.95

therefore by substitution,

log(aK⁺ / aH⁺) = 5.92

Microcline - Halloysite

2KAlSi3O8+ 9H2O + 2H⁺ <-----> 2K⁺ + 4H4SiO4o + Al2Si2O5(OH)4

Keq = (a²K⁺ a⁴H4SiO4^o) / (a²H+)

log(Keq) = 2 (aK⁺ / aH⁺) + 4 loga H4SiO4^o = -7.22

log(aK⁺ / aH⁺) + 2 loga H4SiO4^o = -3.61

Recall, that at quartz saturation, loga H4SiO4^o = -3.95

therefore by substitution,

log(aK⁺ / aH⁺) = 4.29

Albite - Kaolinite

2NaAlSi3O8+ 9H2O + 2H⁺ <-----> 2Na⁺ + 4H4SiO4o + Al2Si2O5(OH)4

Keq = (a²Na⁺ a⁴H4SiO4^o) / (a²H+)

log(Keq) = 2 (aNa⁺ / aH⁺) + 4 loga H4SiO4^o = -0.44

log(aNa⁺ / aH⁺)+ 2 loga H4SiO4^o = -0.22

Recall, that at quartz saturation, loga H4SiO4^o = -3.95

therefore by substitution,

log(aNa⁺ / aH⁺) = 7.68

Albite - Halloysite

2NaAlSi3O8+ 9H2O + 2H⁺ <-----> 2Na⁺ + 4H4SiO4o + Al2Si2O5(OH)4

Keq = (a²Na⁺ a⁴H4SiO4^o) / (a²H+)

log(Keq) = 2 log(aNa⁺ / aH⁺) + 4aH4SiO4^o = -3.71

log(aNa⁺ / aH⁺) + 2aH4SiO4^o = -1.85

Recall, that at quartz saturation, logaH4SiO4^o = -3.95

therefore by substitution,

log(aNa⁺ / aH⁺) = 6.05

Muscovite - Gibbsite

KAl3Si3O10(OH)2+ 9H2O + H⁺ <-----> K⁺ + 3H4SiO4o + 3Al(OH)3

Keq = (a²K⁺ a³H4SiO4^o) / (aH+)

log(Keq) = log(aK⁺ / aH⁺)+ 3 logaH4SiO4^o = -11.16

log(aK⁺ / aH⁺) + 3 logaH4SiO4^o = -11.16

Recall, that at quartz saturation, logaH4SiO4^o = -3.95

therefore by substitution,

log(aK⁺ / aH⁺) = 0.69

Muscovite - Kaolinite

2KAl3Si3O10(OH)2 + 3H2O + 2H⁺ <-----> 2K⁺ + 3Al2Si2O5(OH)4

Keq = (a²K⁺ / a²H⁺)

log(Keq) = 2 log(aK⁺ / aH⁺) = 8.81

log(aK⁺ / aH⁺) = 4.40

Muscovite - Halloysite

2KAl3Si3O10(OH)2+ 3H2O + 2H⁺ <-----> 2K⁺ + 3Al2Si2O5(OH)4

Keq = (a²K⁺ / a²H⁺)

log(Keq) = 2 log(aK⁺ / aH⁺) = -0.99

log(aK⁺ / aH⁺) = -0.49

Microline - Gibbsite

KAlSi3O8+ 7H2O + H⁺ <-----> K⁺ + 3H4SiO4o + Al(OH)3

Keq = (aK⁺ a³H4SiO4^o) / (aH+)

log(Keq) = log(aK⁺ / aH⁺) + 3 logaH4SiO4^o = -7.17

log (aK⁺ / aH⁺) + 3 logaH4SiO4^o = -7.17

Recall, that at quartz saturation, logaH4SiO4^o = -3.95

therefore by substitution,

log= 4.68

Microcline - Muscovite

3KAlSi3O8+ 12H2O + 2H⁺ <-----> 2K⁺ + 6H4SiO4o + KAl3Si3O10(OH)2

Keq = (a²K⁺ a⁶H4SiO4^o) / (a²H+)

log(Keq) = 2 log(aK⁺ / aH⁺) + 6 logaH4SiO4^o = -10.34

log(aK⁺ / aH⁺) + 3 logaH4SiO4^o = -5.17

Recall, that at quartz saturation, logaH4SiO4^o = -3.95

therefore by substitution,

log(aK⁺ / aH⁺) = 6.68

Albite - Gibbsite

NaAlSi3O8+ 7H2O + H⁺ <-----> Na⁺ + 3H4SiO4o + Al(OH)3

Keq = (aNa⁺ a³H4SiO4^o) / (aH+)

log(Keq) = log(aNa⁺ / aH⁺) + 3 logaH4SiO4^o = -5.41

log(aNa⁺ / aH⁺) + 3 logaH4SiO4^o = -5.41

Recall, that at quartz saturation, logaH4SiO4^o = -3.95

therefore by substitution,

log(aNa⁺ / aH⁺) = 6.44

Albite - Muscovite

3NaAlSi3O8+ 12H2O + K⁺ + 2H⁺ <-----> 3Na⁺ + 6H4SiO4o + KAl3Si3O10(OH)2

Keq = (a³Na⁺ a⁶H4SiO4^o) / (aK+ a²H+)

Keq =(a³Na⁺ a⁶H4SiO4^o aH+ ) / (aK+ a³H+)

log(Keq) = 3 log(aNa⁺ / aH⁺) + log(aH⁺ / aK⁺) + 6 logaH4SiO4^o = -5.07

3 log (aNa⁺ / aH⁺) - log(aK⁺ / aH⁺) + 6 logaH4SiO4^o = -5.07

Recall, that at quartz saturation, logaH4SiO4^o = -3.95

therefore by substitution,

3 log(aNa⁺ / aH⁺) - log(aK⁺ / aH⁺) = 18.63

log(aNa⁺ / aH⁺) = 1/3 log(aK⁺ / aH⁺) + 6.21

Albite - Microcline

NaAlSi3O8+ K⁺ + H⁺ <-----> Na⁺ + H⁺ + KAlSi3O8

Keq = (aNa⁺ aH⁺ ) / (aK⁺ aH⁺ )

log(Keq) = log(aNa⁺ / aH⁺ ) + log (aH⁺ / aK⁺ ) = 1.76

log(aNa⁺ / aH⁺ ) - log(aK⁺ / aH⁺ ) = 1.76

log(aNa⁺ /aH⁺ ) = log(aK⁺ /aH⁺ ) + 1.76

Kaolinite - Halloysite

Al2Si2O5(OH)4 <-----> Al2Si2O5(OH)4

log(Keq) = -3.27