Magnetic properties and 57Fe Mossbauer spectroscopy of Mediterranean prehistoric obsidians for provenance studies

Samples from the Mediterranean source-islands: Gyali, Lipari, Melos, Palmarola, Pantelleria and Sardinia (Monte Arci) had their Fe-57 Mossbauer spectra and magnetizations measured. The saturation magnetization (M,) depends on the island of provenance and it reaches a maximum similar to0.3 emu/g for Palmarola obsidians, indicating a larger magnetic phase content. The coercive forces (H-c) range from 46 to 372 Oe for respectively samples from Pantelleria and Palmarola islands. Our analyses show that in a M-r/M-s vs. H-c/H-m, plot the data points accumulate in areas that depend on obsidian provenance (M-r, remanent magnetization; H-m, maximum applied field). The Mossbauer spectra are mainly composed of broad asymmetric doublets, which were fitted assuming two Fe2+ and one Fe3+ sites. In addition, the obsidians of Melos and Palmarola present a magnetic component attributed to magnetite and/or hematite. Binary diagrams comparing different Mossbauer hyperfine parameters for the Fe3+ and Fe2+ species gave indications of similarities and differences between obsidians of different origins. Since this kind of plot does not give an unambiguous characterization of samples from each island, a detailed analysis of the Mossbauer results is in progress using statistical method of clustering analysis as has been shown by Scorzelli et al. [Comptes Rendus Acad. Sci., Serie 11, 332 (2001) 769] and Poupeau et al. [IAOS Bull. 28 (2001) 2] in previous studies. (C) 2003 Elsevier B.V. All rights reserved.