Magnetic properties and 57Fe Mössbauer 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 57Fe M€ossbauer spectra and magnetizations measured. The saturation magnetization (Ms) depends on the island of provenance and it reaches a maximum 0.3 emu/g for Palmarola obsidians, indicating a larger magnetic phase content. The coercive forces (Hc) range from 46 to 372 Oe for respectively samples from Pantelleria and Palmarola islands. Our analyses show that in a Mr=Ms vs. Hc=Hm plot the data points accumulate in areas that depend on obsidian provenance (Mr, remanent magnetization; Hm, maximum applied field). The M€ossbauer spectra are mainly composed of broad asymmetric doublets, which were fitted assuming two Fe2þ and one Fe3þ 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 Fe3þ and Fe2þ 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 M€ossbauer results is in progress using statistical method of clustering analysis as has been shown by Scorzelli et al. [Comptes Rendus Acad. Sci., Serie II, 332 (2001) 769] and Poupeau et al. [IAOS Bull. 28 (2001) 2] in previous studies