Dating Obsidian

There has been a renewed interest in the obsidian dating technique which was developed in the early 1960s. In this dating methodology age determination is related to the thickness of hydration layer in the obsidian artifact. The surface of a freshly carved obsidian artifact slowly absorbs moisture and builds up a hydration rim over a period of time. The rate with which the hydration rim is acquired depends greatly on the composition of the obsidian as well as on environmental factors (28,31,59,60, 73-76). 

Another technique that has been used for dating obsidians, albeit only those that were heated in the past, is the fission track technique (see Textbox 26) (Fleisher et al. 1975). Fission track dating was used, for example, to date the time when an obsidian knifeblade found at a cave in Elmenteita, in Kenya, was heated (see Fig. 24). Since the shape of the blade was distorted, it was deduced that the blade had been heated to a temperature sufficiently high to partially melt it. 

FIGURE 24 Obsidian knife. A knife made of obsidian in Mesolithic times and found in Elmenteita, Kenya, which was heated in the distant past. The time of heating (3700 + 900 years ago) was determined by the fission tracks dating method (see Fig. 25). 

FIGURE 88 Dating methods. Shortly after the discovery of radioactivity, at the beginning of the twentieth century, it was found that the decay of radioactive elements could be used to keep track of time. Many of the dating techniques developed since then are, therefore, based on radioactive decay phenomena, but others, such as the hydration of obsidian, amino acid racemization, and dendrochronology, are based on other physical, chemical, or biological phenomena. 

Friedman, I. and J. Obradovich (1981), Obsidian hydration dating of volcanic events, Quatern. Research 16, 37-47. 

Friedman, I., F. W. Trembour, and R. E. Hughes (1997), Obsidian hydration dating, in Taylor, R. E. and M. J. Aitken (eds.), Chronometric Dating in Archaeology, Advances in Archaeological and Museum Science Series, Vol. 2, Plenum, New York. 

Liritzis, I. (2006), SIMS-SS A new obsidian hydration dating method Analysis and theoretical principles, Archaeometry 48, 533-547. 

Poupeau, G., L. Bellot-Gurlet, O. Dorighel, T. Calligaro, J. C. Dran, and J. Salomon (1996), Obsidian circulation in Prehispanic times in Colombia and Ecuador A coupled PIXE/fission track dating approach, C. R. Acad. Sci., Series Ha, Sciences de la Terre et des Planetes 323(5), 443-450. 

Stevenson, C. M., M. Goitesnian, and M. Macko (2000), Redefining the working assumptions of obsidian hydration dating, /. California and Great Basin Anthropology 22, 223-226. 

The rate of hydration of obsidian, which is diffusion limited, forms the basis for Obsidian Hydration Dating [f]. A date refers to "the time a fresh surface of obsidian was created, either naturally or by man.. ..Laboratory and field studies have confirmed that the time indicated by a hydrated layer is proportional to the thickness squared of the layer. The hydration rate is independent of the relative humidity of the environment, but the chemical composition of the obsidians affect the rate by orders of magnitude. Si02 increases the rate, whereas CaO, MgO, and H20 decrease it. A 6 - 8 °C temperature increase causes doubling of the rate." The method is quite inexpensive, and it is applicable to ages between a few hundred and several million years. 

Erickson, J.E. 1981. Exchange and production systems in Californian prehistory The results of hydration dating and chemical characterization of obsidian sources. British Archaeological Reports International Series, 110, 1-240. 

FIughes, R.E. 1988. The Coso Volcanic Field Reexamined Implications for obsidian sourcing and hydration dating research. Geoarchaeology, 3, 253-265. 

NAA and XRF remain the most widely used techniques for obsidian analysis. However, a wide array of other analytical, geochemical, dating and... 

Bigazzi, G., Ercan, T., Oddone, M., Ozdogan, M. and Yegingil, Z. (1993). Application of fission track dating to archaeometry provenance studies of prehistoric obsidian artifacts. Nuclear Tracks and Radiation Measurements 22 757-762. 

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