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Part I, The Development of the Method*

  • Irving Friedman (a1) and Robert L. Smith (a1)

A freshly exposed surface of obsidian will take up water from the atmosphere to form a hydrated surface layer. This layer has a different density and refractive index than does the remainder of the obsidian. Using special techniques, a thin section of the obsidian cut at right angles to the surface can be prepared. When examined under the microscope the hydrated layer is visible and its thickness can be measured. Photomicrographs of such thin sections are shown. Factors that determine the rate of hydration were considered. Using artifacts from archaeological sites of known age, the influence of temperature, relative humidity, chemical composition of the obsidian, burning and erosion of the obsidian on the rates of hydration was determined. Temperature and chemical composition are the main factors controlling the rate of hydration. Obsidian hydrates more rapidly at a higher temperature, and thus progresses at a faster rate in tropical than in arctic climates. Rhyolitic obsidian hydrates more slowly than does trachytic obsidian. Using archaeological data from various parts of the world, several tentative hydration rates were determined for tropical, temperate, and arctic climates. The method in its present state of development is especially suited to determine relative chronologies in layered sequences of artifacts from a single site, or region. It is also useful for detecting fake artifacts. Future work to refine the method is suggested.

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Publication authorized by the Director, U.S. Geological Survey. A preliminary version of this paper was delivered at the 33rd International Congress of Americanists, July, 1958, San Jose, Costa Rica, and at the annual meeting of the National Academy of Science, May, 1959, Washington, D.C. A more expanded version was read at the 58th annual meeting of the American Anthropological Association, December, 1959, Mexico City.

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Chang, Jen-Hu 1957 Global Distribution of the Annual Range in Soil Temperature. Transactions of the American Geophysical Union, Vol. 38, No. 5, pp. 718–23. Washington.
Friedman, Irving and Smith, R. L. 1958 The Deuterium Content of Water in Some Volcanic Glasses. Geochimica et Cosmochimica Acta, Vol. 15, No. 3, pp. 218–28. New York.
Ross, C. S. and R. L., Smith 1955 Water and Other Volatiles in Volcanic Glasses. American Mineralogist, Vol. 40, pp. 1071–89. Menasha.
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American Antiquity
  • ISSN: 0002-7316
  • EISSN: 2325-5064
  • URL: /core/journals/american-antiquity
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