PHASE PHENOMENA IN CALCITE-SEAWATER SYSTEM 



201 



176 



170 



164 — 



to 

 O 



158 — 



152 



146 



200 400 



PRESSURE, atm 



600 



Fig. 9 Calcium/magnesium in exposed calcite. 



steady state because the composition of the solid solution in contact with the 

 seawater has changed. The solid-solution composition is thus the dependent 

 variable. This need not be so, since the composition dependence can be shared 

 between the solid solution and the liquid solution, but in steady-state systems of 

 this type the composition of the liquid solution is fixed. 



If the pressure and temperature are fixed but the seawater composition is 

 changing, the solid-solution composition must change accordingly if steady state 

 is to be achieved. 



If the seawater composition and the temperature are fixed, a change of 

 pressure requires a change in solid-solution composition for the establishment of 

 a new steady state. 



If the solid-solution composition is changed, with the seawater composition 

 and the temperature fixed, the pressure must be changed to maintain steady 

 state. If one or more of the independent variables is not altered, then the process 

 that results from changing the solid-solution composition will proceed to 

 completion. That is, if the solid solution is higher in magnesium than required 

 for steady state at a given temperature, pressure, and seawater composition, then 

 the pressure must be reduced, the temperature increased, or the magnesium-ion 



