Source characterization, obsidian

Gale, N. (1981), Mediterranean obsidian source characterization by strontium isotope analysis, Archaeometry 23, 41-51. 

Glascock, M. D., G. E. Braswell, and R. H. Cobean (1998), A systematic approach to obsidian source characterization, in Shackley, M. S. (ed.), Archaeological Obsidian Studies Method and Theory, Plenum, New York, pp. 15-65. 

It was not until the application of neutron activation analysis (NAA) that the problem of overlapping sources could be tackled. NAA is a highly sensitive and essentially non-destructive technique, although samples have to be taken which remain radioactive for some time after analysis. The use of NAA in characterizing obsidian was first demonstrated in the early 1970s (Aspinall... 

Before describing the Archaeometry Lab at MURR s involvement in research on obsidian sources and artifacts from South America, some background information on obsidian geochemistry is helpful. In addition, a description of advantages and disadvantages of various analytical methods employed to characterize obsidian is presented. 

Since the mid-1960s, a variety of analytical chemistry techniques have been used to characterize obsidian sources and artifacts for provenance research (4, 32-36). The most common of these methods include optical emission spectroscopy (OES), atomic absorption spectroscopy (AAS), particle-induced X-ray emission spectroscopy (PIXE), inductively coupled plasma-mass spectrometry (ICP-MS), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray fluorescence spectroscopy (XRF), and neutron activation analysis (NAA). When selecting a method of analysis for obsidian, one must consider accuracy, precision, cost, promptness of results, existence of comparative data, and availability. Most of the above-mentioned techniques are capable of determining a number of elements, but some of the methods are more labor-intensive, more destructive, and less precise than others. The two methods with the longest and most successful histoty of success for obsidian provenance research are XRF and NAA. 

Fig. 8.10 Elemental characterization of obsidian sources in Armenia and Anatolia, Turkey. The graph plots the percent of iron vs. the parts per million (ppm) of scandium to show how the amounts of these two elements distinguish the sources of obsidian...

In summary, we have determined LA-ICP-MS analysis to be an accurate and precise instrumental technique for chemical characterization of obsidian artifacts and source samples. We have developed two methods for normalization and standardization of obsidian data that while different, permit LA-ICP-MS data to be transformed to abundance data and that data derived by LA-ICP-MS conq>ares favorably to INAA data. The minimal sanq>le preparation time, the ability to select the suite of elements that will be analyzed, and the rapid analytic time make LA-ICP-MS, a minumUy invasive, cost-effective method for characterizing obsidian. 

Williams-Thorpe, O., S. E. Warren, and J. G. Nandis (1997), Characterization of obsidian sources and artefacts from central and eastern Europe, using instrumental neutron activation analysis, in Korek, J. (ed.), Proc. Int. Conf. Lithic Raw Material Characterization, Budapest and Siimeg, 1996, Budapest. 

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. 

For the reasons outlined above, outcrops of workable obsidian are relatively few in number and are restricted to areas of geologically recent lava flows. Most sources are therefore reasonably well known, and, because of these constraints, identification of new sources in the eastern Mediterranean region becomes ever more unlikely. This makes the exercise of characterizing archaeological obsidians an attractive proposition, since, unlike potential clay sources for pottery provenance, the existence of completely unknown sources can be (cautiously) ignored. This is, of course, subject to the requirement noted above for more detailed geochemical characterization of existing sources. 

Not all rocks can be characterized as successfully as obsidian. The success of obsidian provenance is due to the limited number of workable sources and the fact that each source, while being relatively homogeneous, is sufficiently different from other sources to enable elemental fingerprinting . This picture contrasts markedly with that of, for example, flint a stone not restricted to a... 

Tykot, R.H. (1997). Characterization of the Monte Arci (Sardinia) obsidian sources. Journal of Archaeological Science 24 467-479. 

Gratuze, B. (1999). Obsidian characterization by laser ablation ICP-MS and its application to prehistoric trade in the Mediterranean and the Near East sources and distribution of obsidian within the Aegean and Anatolia. Journal of Archaeological Science 26 869-881. 

Archaeologists have long sought methods for obsidian characterization that were rapid, reliable, non-destructive, and low-cost. Among the various methods investigated were visual techniques (79), density measurements (20), magnetic properties (27), thermoluminescence (22), fission-track analysis (25), Mossbauer spectroscopy (24), and natural radioactivity (25). Although some of the methods occasionally identified differences between sources, the overlap between sources was such that their overall reliability was unsatisfactory. The most successful method of characterization for obsidian provenance research has been compositional analysis (26). 

This investigation focuses on obsidian reaching two highland Iranian sites during the tinje period from roughly 3500 to 1800 B.c. Geological source samples from two major source regions in Western Asia were used to characterize possible sources of the artifacts. 

This study has demonstrated that precise chemical analysis is a powerful tool for the characterization and provenance determination of Middle Eastern obsidian. Thirteen to 15 chemically distinctive groups were distinguishable in geological source samples collected from eight source... 

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