The 18O/16O fractionation accompanying the hydrothermal crystallization of quartz from silicic acid at 265°-465°C has been studied in order to assess the influences of (a) rate of quartz formation, (b) the nature of the reaction mechanism, and (c) temperature. At 360° and 465°C there are no indications of rate effects influencing isotope partitioning, but at 265°C (where fractionation factors show an unusually large scatter) the evidence is inconclusive in this respect. All reaction appears to occur through solution-precipitation processes, with the intermediate phases, cristobalite and silica K, giving identical fractionation factors (within experimental errors) to quartz samples formed at the same temperature. The temperature-dependence of fractionation in the range 265°-465°C is given by the equation

103ln α(SiO2H2O)=3.05×106T22.09

The data are in good agreement with other experimental calibrations of the quartz-water fractionation.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.