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

Abstract

Users of the obsidian hydration dating method have routinely assumed that artifacts which originate from the same geological flow will be of the same chemical composition and thus hydrate at the same rate under equivalent conditions of temperature and relative humidity. Recent laboratory experimentation into the hydration process has shown that the intrinsic water content of the glass is the dominant factor in establishing the rate of hydration. Water content determinations on a large suite of samples from numerous prehistoric quarries within the Coso volcanic field, California, indicated that water content values, and thus hydration rate, varied significantly on a within flow basis. It is recommended that water determinations be made on individual artifacts prior to obsidian hydration dating. 0 1993 John Wiley & Sons, Inc.

Obsidian hydration at high elevation: Archaic quarrying at the Chivay source, southern Peru

“…Chemical reactions within obsidian slow considerably with colder temperatures, thus, the slow hydration rate is largely expected (Friedman and Trembour, 1983;Stevens, 2005). However, the slow hydration rate could also be caused by chemical properties of Chivay obsidian, such as lower concentrations of intrinsic water (Liritzis, 2006;Rogers and Duke, 2011;Stevenson et al, 2000;Stevenson et al, 1993). In sum, we lack the chemical, climatic and comparative hydration data to determine the ultimate cause of the slow hydration rate at Maymeja.…”

“…Rogers, 2007;Stevenson et al, 1993). Using this result, we apply a binomial regression to the hydrationeradiocarbon pairs at A03-330, anchoring the curve at the origin.…”

Archaeological Age Estimation Based on Obsidian Hydration Data for Two Southern Andean Sources

“…Granting that intrinsic water content can vary considerably within sources (Stevenson et al 1993), each sample was assigned to a source group based on its geochemical composition in a first-order attempt to control for the effects of intrinsic water on hydration rate. Geochemical composition was determined by a Bruker hand-held energy-dispersive XRF spectrometer (EDXRF), calibrated using "well-characterized source samples in the MURR reference collection… previously analyzed by NAA and XRF in several laboratories to establish consensus values" (Glascock and Ferguson 2009:3).…”

“…These techniques are not yet widely used in archaeology, and anhydrous glass chemistry is a common alternative means of controlling for inherent differences by grouping sources/flows based on physical or, preferably, geochemical properties (as determined by X-ray fluorescence spectroscopy or neutron activation analysis, for example ;Bettinger 1989;Eerkens, Spurling and Gras 2008;Ericson 1989;Liritzis 2006). Anhydrous glass chemistry should be used cautiously, however, since intrinsic water content has been shown to vary considerably even within flows (Stevenson et al 1993).…”

The significance of obsidian hydration dating in assessing the integrity of Holocene midden, Hokkaido, northern Japan

“…Although the effect of geochemical variation on hydration rate has been investigated in the earlier days of research (Friedman and Long, 1976;Friedman and Trembour, 1983;Suzuki, 1971), recent investigations regard the water content as the significant endogenous factor (e.g., Rogers, 2008bRogers, , 2013Steffen, 2005;Stevenson et al, 1998;Zhang et al, 1997). For example, empirical studies of measuring water content of obsidian suggest that intrinsic water content of individual obsidian specimens are varied not only between the sources but also within a single source (Stevenson et al, 1993, see also Hughes, 1988. Given the variation in intrinsic water content in between geochemical sources of obsidian sources, it is strongly recommended that chemically distinctive sources need to be distinguished before calculating dates to control the effect of inter-source variation of intrinsic water content (Rogers, 2007).…”