The Experimental Hydration of Obsidian as a Function of Relative Humidity and Temperature

Abstract

The experimental hydration of obsidian for up to 30 days is described at relative humidities (RH) of 60, 90, 95, and 100 percent and at temperatures of 150, 160, and 175°C. Under isothermal conditions, the rate of hydration increased by as much as 25 percent between 60 and 100 percent RH. The RH dependence is nonlinear, with the majority of the rate increase occurring between 90 and 100 percent RH. The effect of RH can be related to the driving force for molecular water diffusion in obsidians as described by the chemical potential difference between water sorbed onto the obsidian surface and intrinsic water in the obsidian. The differences in hydration rates caused by RH differences in experiments approximate the error commonly described for obsidian-hydration dating. These results suggest that obsidian-hydration dating requires a knowledge of the site temperature and relative humidity in order to accurately generate age estimates.

The effects of the glass surface area/solution volume ratio on glass corrosion: A critical review

“…Nevertheless, defects in the silicate structure may provide diffusion channels large enough to permit molecular water diffusion. For example, water diffusion is known to occur without affecting the silicate network of obsidian [20][21][22][23]. In most instances, tests of alkali silicate glasses in silicate solutions also show dealkalization to occur without affecting the silicate network [24].…”

Homogeneity of water content in obsidian from the coso volcanic field: Implications for obsidian hydration dating

“…The birefringent layer formation proceeds at a rate that is constant as a function of the square root of time (Friedman and Long, 1976;Mazer et al, 1991) and is a result of the inward diffusion of molecular water into the glass network, in this article referred to as "hydration" (Friedman and Long, 1976;Lee et al, 1974;Mazer et al, 1992;Zhang et al, 1991). The birefringence of this layer is thought to arise from strain introduced into the glass network during hydration (Marshall, 1961;Ross and Smith, 1955).…”

“…Recent experimental studies indicate that there is a strong correlation between a single compositional parameter, the logarithm of the bulk intrinsic water content, and the obsidian hydration rate at temperatures ranging between 110" and 240°C (Mazer et al, 1991(Mazer et al, , 1992. In these studies, intrinsic water content referred to the total OH-and H20 species measured with infrared spectroscopy using the quantification methods described by Newman et al (1986).…”

“…The obsidians within this field have also been the focus of studies of trace element chemistry (Bouey, 1991;Hughes, 1988) and obsidian hydration rates (Friedman and Long, 1976;Ericson, 1989;Mazer et al, 1991;Stevenson and Scheetz, 1989). The existing data from the Coso field suggest: (1) Intrinsic water contents vary within and between obsidian flows (Bacon et al, 1981); (2) a large number of hydration rates derived from Coso obsidians have been reported (Ericson, 19881, and (3) potassium-argon radiometric dating of obsidian from this field are in fair agreement with dates generated by the Chemical Index correlation method (Duffield et al, 1980).…”

“…The relative humidity of the hydrating environment has also been shown to have a significant effect on obsidian hydration (Mazer et al, 1991). Estimates of the ambient temperature and relative humidity for unknown samples are inserted into the Arrhenius equation to relate birefringent layer thickness to age before present (Stevenson and Scheetz, 1989;Mazer et al, 1991).…”