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

Published online by Cambridge University Press:  20 January 2017

J. J. Mazer
Affiliation:
Argonne National Laboratory, Argonne, IL 60439-4837
C. M. Stevenson
Affiliation:
Archaeological and Historical Consultants, Inc., P.O. Box 482, Centre Hall, PA 16828
W. L. Ebert
Affiliation:
Argonne National Laboratory, Argonne, IL 60439-4837
J. K. Bates
Affiliation:
Argonne National Laboratory, Argonne, IL 60439-4837

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.

Résumé

Résumé

Se describe la hidratación experimental de obsidiana por hasta 30 días, a humedades relativas (HR) de 60, 90, 95, y 100 por ciento y a temperaturas de 150, 160 y 175°C. En condiciones isotérmicas, el grado de hidratación aumentó hasta un 25 por ciento entre 60 y 100 por ciento de HR. El efecto de la HR puede estar relacionado con la fuerza que impulsa la difusión molecular del agua en obsidianas, descripta por la diferencia en elpotencial químico entre el agua absorbida en la superficie y el agua intrínseca en la obsidiana. La diferencia en los grados de hidratación causada por diferencias en HR durante los experimentos se aproxima al error comunmente descripto para la datación por hiratación de obsidiana. Estos resultados sugieren que la datación por hidratación de obsidiana requiere el conocimiento de la temperatura y humedad relativa del sitio a fin de generar estimaciones de antigüedad exactas.

Type
Reports
Copyright
Copyright © The Society for American Archaeology 1991

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