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Equilibrium fractionation factors for the distribution of 18 0 between alkaline-earth carbonates and water have been measured over the temperature range G-500°C. The fractionation factors a: can be represented by the equationsCaCO.-H20, Measurements on MnCO., CdCO., and PbCO. were made at isolated temperatures. A statistical-mec~anical calculation of the isotopic partition function ratios gives reasonably good agreement with expenment. Both cationic size and mass are important in isotopic fractionation, the former predominantly in its effect on the internal vibrations of the anion, the latter in its effect on the lattice vibrations.

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Equilibrium constants for oxygen isotope exchange between quartz and water have been measured from 195°C (1000 ln α = 12.0) to 750°C (1000 ln α = 0.4). Over limited temperature ranges the behavior of fractionation with temperature can be approximated by 1000 ln α = 3.38 (106 T−2) − 3.40 for 200°–500°C and by 1000 ln α = 2.51 (106 T−2) − 1.96 for 500°–750°C. The results of measurements in the quartz‐water system can be combined with analogous results from other mineral systems to make mineral‐pair isotopic thermometers for application to problems of petrogenesis.

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