Oxygen isotope fractionation accompanying the hydrothermal crystallization of quartz from silica gel has been studied at temperatures between 180 degrees and 550 degrees C under salinities of 0, 5, 25, and 40 wt percent to assess the effect of the salinity, the delta i value, the reaction mechanism, and the temperature on the isotope fractionation. The findings suggest that oxygen isotope equilibrium between silica gel and pure water at low temperatures cannot be established. Factors affecting the exchange rate between oxygen-bearing phases include salinity of solution, delta i value, and temperature. The authors of this paper do not agree with the conclusion on salt isotope effect reached by Truesdell (1974).The temperature dependence of oxygen isotope fractionation between quartz and water from 180 degrees to 550 degrees C and salinities of 5, 25, and 40 wt percent is 1,000 ln alpha (sub Q-H 2 O) = 3.306 X 10 6 T (super -2) - 2.71.

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