Antigorite Chemical Formular in the PITZER & LLNL Databases

[shameer]

Hi,

I have come across the antigorite mineral when using the Pitzer and LLNL databases.
The dissolution reaction and thermodynamic data is shown below.

My question is about the chemical formula, which is very different from the formula of Antigorite from webmineral (Mg)3Si2O5(OH)4?

Antigorite
#        Mg48Si24O85(OH)62 +96.0000 H+  =  + 34.0000 SiO2 + 48.0000 Mg++ + 79.0000 H2O
        log_k           477.1943
   -delta_H   -3364.43   kJ/mol   # Calculated enthalpy of reaction   Antigorite
#   Enthalpy of formation:   -17070.9 kcal/mol
        -analytic -8.1630e+002 -6.7780e-002 2.5998e+005 2.2029e+002 -9.3275e+006
#       -Range:  0-300

[Rasmus]

- it is a phyllosilicate implying plenty of possibilities for substitutions and variations - my guess is that the Antigorite data in the LLNL database is derived from a specific experiment with an Antigorite with this specific composition. In general - don't expect too much from calculations (in terms of absolutely precise results) on this type of minerals....

[shameer]

thank you!