Epsilon iron oxide: origin of the high coercivity stable low Curie temperature magnetic phase found in heated archeological materials

The identification of epsilon iron oxide (ɛ-Fe2O3) as the low Curie temperature high coercivity stable phase (HCSLT) carrying the remanence in heated archeological samples has been achieved in samples from two archeological sites that exhibited the clearest evidence of the presence of the HCSLT. This uncommon iron oxide has been detected by Confocal Raman Spectroscopy (CRS) and characterized by rock magnetic measurements. Large numbers of ɛ-Fe2O3 microaggregates (in CO) or isolated clusters (in HEL) could be recognized, distributed over the whole sample, and embedded within the ceramic matrix, along with hematite and pseudobrookite and with minor amounts of anatase, rutile, and maghemite. Curie temperature estimates of around 170°C for CO and 190°C for HEL are lower than for pure, synthetic ɛ-Fe2O3 (227°C). This, together with structural differences between the Raman spectra of the archeologically derived and synthetic samples, is likely due to Ti substitution in the ɛ-Fe2O3 crystal lattice. The γ-Fe2O3-ɛ-Fe2O3-α-Fe2O3 transformation series has been recognized in heated archeological samples, which may have implications in terms of their thermal history and in the factors that govern the formation of ɛ-Fe2O3

The fission-trackanalysis: An alternative technique for provenance studies of prehistoric obsidian artefacts

Agence de Developpement Economique du Doubs;Region de Franche-Comte;Societe Francaise de Chimie;Universite de Franche-Comt;Ville de BesanconProceedings of the 1998 19th International Conference on Nuclear Tracks in Solids (ICNTSs) --31 August 1998 through 4 September 1998 -- Besancon --Comparison of fission-track parameters - age and track densities - is an alternative tool for correlating obsidian artefacts with their potential natural sources. This method was applied by different fission-track groups in various regions and results were compared with those obtained using the more popular provenance identification techniques based on chemical composition studies. Hundreds of analyses prove that fission-track dating is a complementary technique which turns out to be very useful, specially when the chemical composition does not fully discriminate different sources. Archaeologically significant results were obtained applying the fission-track analysis in various regions of earth. © 1999 Elsevier Science Ltd. All rights reserved

Inside black pearls

The quality of natural and cultured pearls depends on the size, shape and properties of the surface. The inner structure of the pearl is not known, and not taken into account. Indeed, it is assumed that the cultured pearl is a nucleus covered by a thin organic layer, a thin prismatic layer and a thick nacreous layer. The examination of spherical and pear shape samples resulting from the grafting of the black lip pearl oyster (Pinctada margaritifera) shows that this assumption is, in most cases, erroneous. Optical, electron and atomic force microscopic observations, infrared and Raman analyses, as well as micro X-ray fluorescence and micro X-ray absorption near-edge spectroscopy data show that the inner structure of a pearl does not depend on its shape. Both circle or pear shape and spherical pearls show a large variability of the inner structures and composition. There are no two identical samples. Moreover, the arrangement is irregular within a single pearl, and some structures (aragonitic pseudo-prisms) do not exist in the shell

New data and provenance of obsidian blocks from Middle Neolithic contexts on Corsica (western Mediterranean)

The provenance of twelve un-worked blocks and one part-knapped block recovered from the surface of five Middle Neolithic sites in the vicinity of Porto Vecchio, southeastern Corsica (western Mediterranean), was determined by ion beam analysis (PIXE). This is the first such discovery on Corsica of actual raw blocks of this exotic material. Twelve of these samples come from sources associated with the Monte Arci volcanic complex of Central-West Sardinia, with six each of the SA and SC chemical types. The only possible origin for the remaining block is Lipari, a raw material previously only attested by three artifacts from a Neolithic site of NW Corsica. This piece is aberrant for its unusual facies and its poor quality, making it quite unsuitable for knapping, and by extent distinct from the high quality glassy obsidian from Lipari that was used regularly by Neolithic peoples. This raises the question of the archaeological significance of this surface find