Chalcedony, 244 solubility

Several chemical geothermometers are in widespread use. The silica geothermometer (Fournier and Rowe, 1966) works because the solubilities of the various silica minerals (e.g., quartz and chalcedony, Si02) increase monotonically with temperature. The concentration of dissolved silica, therefore, defines a unique equilibrium temperature for each silica mineral. The Na-K (White, 1970) and Na-K-Ca (Fournier and Truesdell, 1973) geothermometers take advantage of the fact that the equilibrium points of cation exchange reactions among various minerals (principally, the feldspars) vary with temperature. 

The common silica rocks, chert and chalcedony, are made up of fine-grained quartz and microcrystalline silica. Accordingly, their solubility exceeds that of well-crystallized quartz. Fournier (1985) suggests the temperature function... 

Fig. 1.18 Temperature dependence of the solubility of a-quartz, chalcedony, a-cristobalite, moganite, p-cristobalite and amorphous silica at different pressures, as specified (data computed by SUPCRT92). Also shown is the temperature dependence of the solubility of an unspecified tridymite (data from Wagman et al. 1982) (Marini 2007)...

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