Obsidian hydration dating archaeology
In its natural state, it has a thick rind formed by the diffusion of the water into the atmosphere when it first cooled--the technical term is "hydrated layer".When a fresh surface of obsidian is exposed to the atmosphere, as when it is broken to make a stone tool, more water is released and the rind begins to grow again.However, in spite the accurately measured rinds beyond digital optical microscopy employing infrared spectroscopy and nuclear analysis, the traditional empirical age equation produce occasionally satisfactory results but still fail to produce a reliable chronometer.In the last ten years, secondary ion mass spectrometry (SIMS) has been employed to accurately define the hydration profile.Discussions are given of techniques for measuring the hydration thickness, measurement (or estimates) of ambient hydration temperature, chemical composition of the obsidian, and the conversion of hydration thickness to dating the time of manufacture of the artifact. Comparisons are made between the results of obsidian hydration and other dating methods. By measuring the thickness you can easily determine if one artifact is older than another (relative age).
► New approaches of hydrated surface layer by using Fick's law of diffusion.
The potential of the method in archaeological chronologic studies was quickly recognized and research concerning the effect of different variables on the rate of hydration has continued to the present day by Friedman and others. In Chronometric Dating in Archaeology, edited by R.
When this hydrated layer or rind reaches a thickness of about 0.5 microns, it becomes recognizable as a birefringent rim when observed as a thin section under a microscope.
The relationship is disarmingly simple: Age = DX2, where Age is in years, D is a constant and X is the hydration rind thickness in microns.
Obsidian hydration dating (OHD) is a geochemical method of determining age in either absolute or relative terms of an artifact made of obsidian.
The effects of these variables have often been summarized and will not be discussed further here (Michels and Tsong 1980; Friedman and Obradovich 1981; Freter 1993; Hull 2001; Stevenson et al., 1993, 1998, 2000; Friedman et al. 1999, Ridings 1996; see Skinner and Tremaine 1993 for additional references).