Na2O-FeO-Al2O3-SiO2   &   K2O-FeO-Al2O3-SiO2

Riebeckite thermodynamic data are now fitted to experiments of Ernst (1962) for the reaction rieb + 3hem = 2acm + 3mt + 4q + H2O. This equilibrium relies on the availability of data for acmite, which were retrieved on the basis of the reaction 2acm + pa + 2q = 3ab + hem + H2O. No experiments are available for this reaction, but it has occurred in the Eastern Alps at around 9 kbar and 450°C (Holland & Ray, 1985) in an assemblage with pure albite, hematite, paragonite and a sodic pyroxene of composition jadeite{44}acmite{56}. Thus data for both acmite and riebeckite must be regarded as provisional.

Data for ferroglaucophane are now fitted to the experiments of Hoffmann (1972) on the reaction 2fgl = 4abh + 3fa + q + 2H2O. These data are in agreement with the Fe-Mg exchange equilibria seen in natural assemblages (see the exchange section of table 7).

Data for annite, derived from the exchange reaction of Ferry & Spear (1978) also fit the experiments of Holdaway & Lee (1977) for the reaction 2ann + 6sill + 9q = 2san + 3fcrd + 2H2O.

241)  2fgl = 4abh + 3fa + q + 2H2O   (Hoffmann, 1972)
 
  ln_K  x(CO2)  P(kbar)      T(C)     H(low) H(high)  miss   calc   2sd        summary
     0     0      3.0     340  370   247.91  257.62           351    28   2 (243.13 <-> 247.91)
     0     0      5.0     350  370   236.77  243.14     27    397    30   cH = 251.49 (sd  5.22) 3
                                                                          too high but OK
                                                                          uH = 1.71, d/s = -1.4, h = 0.47
 
242)  rieb + 3hem = 2acm + 3mt + 4q + H2O   (Ernst, 1962)
 
  ln_K  x(CO2)  P(kbar)      T(C)     H(low) H(high)  miss   calc   2sd        summary
     0     0      0.5     465  490   104.46  108.10           485     8   3 (106.57 <-> 108.18)
     0     0      1.0     489  499   106.48  107.86           495     8   cH = 107.38 (sd  0.56) 
     0     0      2.0     511  516   107.71  108.38     -2    509     8   within bracket
                                                                          uH = 0.68, d/s = 0.1, h = 1.00
 
*  2ann + 6sill + 9q = 3fcrd + 2san + 2H2O   (Holdaway & Lee, 1977)
 
  ln_K  x(CO2)  P(kbar)      T(C)     H(low) H(high)  miss   calc   2sd        summary
  1.60     0   2.1  1.9     640      270.85  273.32  -0.30   1.60  0.29    ** NOT USED **
  1.60     0   2.8  2.6     710      276.20  278.60          2.72  0.31   cH = 277.19 (sd  2.70)