Mössbauer and XRD study of Roman amphorae buried in the sea for two millennia

Summary

A decade ago Roman Haltern 70 amphorae were found in the sea near Cortiçais on the Atlantic coast of Portugal. They stem from a shipwreck dated to between 15 BC and 15 AD. We have studied fragments of these amphorae by Mössbauer spectroscopy and X-ray diffraction to look for changes caused by two millennia of exposure to seawater. For comparison we studied Haltern 70 type amphorae excavated on land at Castro do Vieito in the north of Portugal. The sherds show a layer structure with 2 to 3 mm thick soft buff outer layers and a harder gray core. The different layers were studied by Mössbauer spectroscopy and X-ray diffraction. The Mössbauer spectra of the surface layers show that up to 80 % of the iron is present as goethite particles which are superparamagnetic at room temperature but exhibit magnetically split spectra at 4.2 K. The goethite is too fine-grained to be detected by X-ray diffraction. The spectra of the cores contain up to 40 % of ferrous iron and resemble those of the land-buried amphorae. The results show that the iron in the outer layers of the sherds converted to goethite under the prolonged influence of the seawater.

This Resource is Part of the Following Collections

• Society for American Archaeology 81st Annual Meeting, Orlando, FL (2016)

Keywords

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