I have tried modelling siderite-magnesite solid solutions using the community version of GWB. I decided to check the properties of various carbonates used in model calculations, including calculation of molar volumes for pure carbonate phases from unit cell parameters. I obtained generally good agreement with GWB properties listed for calcite, magnesite and rhodochrosite, but found a large difference between the GWB value (28.630 cm3/mol) and a value calculated from unit cell data (29.376 cm3/mol) for siderite.
Also, I don't appear to be able to access the continuous SS modelling option in the community version.
Would anyone care to comment?