Obsidian and Stone Sourcing - Keys to Prehistoric Trade Networks

Stone tools and objects are a sustaining record of ancient societies. The morphologies and use-wear of stone tools provide insight into methods of manufacture, intended function, and actual use by pre-historic communities. The compositions of stone tools – at a basic level the rock type, and at deeper levels the abundances of certain trace elements – are keys to linking objects to the locations of source raw materials, and from there establish otherwise forgotten details about exchange networks that existed throughout history.

Obsidian sourcing is a well established method employed by archaeologists and anthropologists that has allowed trade distribution networks to be studied in the Mediterranean, the Americas, the Southwest Pacific, and in many other places. Being a volcanic glass, the physical properties of obsidian made it ideal for the manufacture of sharp edges, to be used as knives, scrapers, and spear or arrow points, while remaining resistant to breakage. But the rare property of obsidian that is advantageous to archaeologists is that it occurs in volcanic flows that are remarkably homogeneous in chemical composition within a flow, but preserve elemental signatures that are unique to volcanic centers, and in some cases individual flows. This provides the potential to trace worked obsidian right back to its place of origin.
 

Lying at the intersection between scientific, historical and cultural importance, destructive compositional analysis and removal of artifacts from archaeological sites is rarely an option. Analytical solutions for such work need to be portable and easy to use.

The TRACER 5 handheld-XRF by Bruker Nano Analytics provides a tool tailored for non-destructive analysis in almost any environment – on-site, in a collections space, or in the lab. The TRACER 5 allows quantification of the primary trace elements of importance for obsidian sourcing, such as rubidium (Rb), strontium (Sr), zirconium (Zr), yttrium (Y), and niobium (Nb). Fe (iron), copper (Cu), zinc (Zn), as well as any additional minor and major elements that may help assign artifacts to probable sources of raw materials.

Quantification of a trace element suite focused specifically on obsidian sourcing is provided by a matrix-matched calibration developed in collaboration with the Missouri University Research Reactor (MURR) Archaeometry Laboratory, that allows rapid determination of trace element compositions without the need for post-processing.
 

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Detecting exchange networks in New Britain, Papua New Guinea: geochemical comparisons between axe-adze blades and in situ volcanic rock sources

Penguilley, A., Brand, C., Flexner, J., Specht, J., Torrence, R.
Archaeology in Oceania, 54, 200-213, 2019

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Examination of Heritage and Geological Materials Using Correlated Electron- and X-ray-Beam Microanalysis in the SEM

Vicenzi, E., Lam, T.
Microscopy & Microanalysis, 25 (Suppl 2), 2482