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

Abstract

Samples from the Mediterranean source-islands: Gyali, Lipari, Melos, Palmarola, Pantelleria and Sardinia (Monte Arci) had their 57Fe Mössbauer 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 Mössbauer 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 Mössbauer 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 Mössbauer 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.