Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Obsidian is a natural volcanic glass which was one of the most appreciated materials by of ancient man for cutting tools and has been found by researchers in many locations, far away from any natural source. Reliable provenancing can provide evidence of contacts over a certain distance and information about exchange patterns and mobility of prehistoric people.
The application of analytical methods can solve the problem of obsidian provenancing by means of its highly specific chemical composition, the “chemical fingerprint”. Combined external Ion Beam Analysis (IBA) measurements, consisting of Proton Induced X-ray Emission (PIXE), Proton Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), are frequently used due to the high sensitivity and the non-destructive beam mode. Our study has been carried out at the 5 MV Tandem accelerator of the Ion Beam Centre of FZD, where a number of quantitative glass analyses has been performed simultaneously with all three external ion beam techniques [1-5].
Obsidian usually exhibits a very uniform appear-ance and is generally described as a relatively homogeneous material. Banded obsidians can be observed also, and the question was raised, if these bands are caused by differences in the chemical composition or if these changes in the optical properties are related to inclusions of clouds of gas bubbles, microphenocrysts or similar features without significant compositional influence. Therefore, a systematic investigation of a banded obsidian sample from Demengakion (Milos, Greece) has been carried out in order to check the actual variation range of the chemical composition. (Fig. 1).
To investigate the influence of different preparation techniques on the analytical results, we produced an obsidian in-house reference sample (Fig. 2). This specimen originates from the highly homogeneous obsidian source Hrafntinnuhryggur (Iceland) and features three different surfaces: natural fracture, ground finish (1200 diamond lap) and polished [6].
This study is part of a project which aim is to apply selected analytical methods, in particular IBA, Neutron Activation Analysis (NAA) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), to detect a maximum of compositional differences between easily available samples of the natural obsidian sources in Europe. This knowledge should enable to decide, which least invasive analytical method should be chosen for the analysis of a specific archaeological artefact, on a case by case basis.
References: [1] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136–146. [2] Mäder M. et al. NIMB 239 (2005) 107-113. [3] Mäder M. and Neelmeijer C. NIMB 226 (2004) 110–118. [4] Jembrih D. et al. NIMB 181 (2001) 698–702. [5] Mäder M. et al. NIMB 136-138 (1998) 863–868. [6] Tuffen H. and Castro J. M. Journal of Volcanology and Geothermal Research 185 (2009) 352–366.