MAGNETIC PROPERTIES OF CENTRAL MEDITERRANEAN OBSIDIANS: AN ARCHAEOLOGICAL FINGERPRINT?

Archaeological provenance studies can help to understand economic and social interactions in antiquity. Tykot (2002) has sourced obsidians from the central Mediterranean with chemical fingerprinting methods. NAA, XRF, and LA-ICP-MS have allowed characterization of obsidians from islands and subsources therein. Other research has demonstrated the potential use of magnetic properties to provenance obsidians in this region (McDougall et al., 1983). If this non-destructive method is successful, archaeologists could use magnetic provenance techniques on site and reduce the preparation and measurement time associated with chemical methods. Our study further investigates the viability of magnetic property provenancing in the central Mediterranean.

Tykot (2002) has documented in detail the four Italian islands with geological sources of obsidian. We measured the following magnetic properties of 30 geologic obsidian samples collected from outcrops on the islands: low frequency susceptibility per unit mass (median (med)=27 SI, Interquartile range (IQR)=76 SI); high frequency susceptibility per unit mass (med=25 SI, IQR=70 SI); percent frequency effect (med=9.6 %, IQR=22 %); natural remanent magnetization (med=.38 A/m, IQR=1.7 A/m); demagnetization properties; median destructive field (med=980 Oe, IQR=420 Oe); induced remanent magnetization properties; saturation remanent magnetization (med=15 A/m, IQR=63 A/m); and backfield coercivity of remanence (med=68 mT, IQR=37 mT). Bivariate plots and multivariate statistics help to establish the properties that best distinguish the sources.

Preliminary results suggest that magnetic properties can be used to provenance obsidians to islands and some subsources in the central Mediterranean. However, measurement of more samples is required to better define the ranges of the geologic obsidians’ properties. Once more fully characterized, archaeological obsidian samples that have been geochemically provenanced could be tested to assess the magnetic fingerprinting method.