Oxygen isotope studies of zeolites—Stilbite, analcime, heulandite, and clinoptilolite: III. Oxygen isotope fractionation between stilbite and water or water vapor

Abstract

The oxygen isotope fractionation between the aluminosilicate framework of stilbite and water vapor (or bulk water) was studied between 125 and 300°C. The fractionation factor for exchange between the channel water of stilbite and water vapor was determined at room temperature. At this temperature, the channel water of stilbite is enriched in 18O by 6%. relative to water vapor (and hence is depleted in 18O by 3%. relative to the liquid water). Reliable values of the fractionation between framework oxygen and water vapor were obtained only at 220°C and higher temperatures. At these temperatures, the fractionation is described by the equation: 1000 In α stilbite-water = −2.4 + 2.7 × 10 6 T 2 . The measured fractionation factors are similar to the fractionation factors in the albite-water system extrapolated from values measured at higher temperatures (≥ 350°C). This observation is consistent with the fact that the stilbite has the same Al Si ratio as albite.