LECTURES ON GEOCHEMICAL !N1 ERPRETATION OF ...

- 33 -GEHERAL EQUATION FOR SOLUBILITY OF QUARTZ IH WATER. STKAK. AYD SALINESOLUTIONS APPLICABLE FROM 25· TO 900·CThe solubility of quartz in water in the temperature range 25· to 900·Cat specific volume (V) of the solvent ~angingfrom about 1 to 10 and from300· to 600·C at specific volume of the solvent ranging from about 10 to100 can be calculated using the following equations from Fou~ier andPotter (1982a), where m is molality dissolved silica and T is temperaturein kelvins:2Log m = A + B(log V) + e(lot V)(14)-1A = - 4.66206 + 0.0034063 T + 2179.7 T_ 1.1292 x 10 6 T- 2 + 1.3543 x 10 8 T- 3(15)8 = - 0.0014180 T _ 806.9 T- 1(16)- 4C = 3.9465 x 10T(17)The solubility of quartz in natural saline solutions can be calculatedusing equation (14) when (- log pF) is substituted for (log V), where p isthe density of the solution and F is the weight f~action of water in thatsolution (Fou~nlc~, 1983). Hote, however, that dissolved silica appca~sto form a complex with sulfate in sodium sulfate solutions, so additionalcalculations and adjustments a~e ~equired when dealing with sulfate- richb~ines (see Fou~ier and Marshall, 1983).SOLUBILITY OF AMORPHOUS SILICA AT RXTRRKR CONDITIOHSEquation (6) can be rearranged to give the solubility of amorphoussilica as a function of temperature for the range o· to 250·C at the vaporpressure of the solution:Log S ~ {- 131fT I + 4 . 52 , (lB)where S is the concentration of dissolved silica in mg/kg and T is