Characterization of two Roman coins from an archaeological site in Portugal

✍ Scribed by A. L. Mata; M. M. L. Salta; M. M. M. Neto; M. H. Mendonça; I. T. E. Fonseca

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: German
• Weight: 318 KB
• Volume: 61
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.200905284

✦ Synopsis

This paper reports a study carried out on two Roman coins found in the archaeological site of Sa ˜o Pedro, in Fronteira (Alentejo, Portugal). One coin was in a quite well preserved state, allowing its reading and historical identification, while the other was quite deteriorated and its reading difficult. The coins have been identified as: an Antoninianus of Galilenus (267-268 A.D.) and an AE 3 (337-340 A.D.) in which is impossible to identify the emperor. Energy dispersive spectroscopy (EDS) has given the following average composition:

for the outer layers of the Antoninianus and of the AE 3, respectively. The exact substrate composition of the AE 3 could be determined

The chemical composition found for the AE 3 is consistent with historical investigations, since silver-plated Cu-Pb-Sn alloys was the material used in the production of the AE 3. X-ray powder diffraction spectroscopy (XRD) has identified as possible crystalline compounds: a mixture of two silicates, namely the lead aluminium silicate, Pb 4 Al 4 Si 3 O 16 , and the lead copper silicate, Pb 8 Cu(Si 2 O 7 ) 3 , pyromorphite, Pb 5 (PO 4 ) 3 Cl, on the Antoninianus and only oxides, namely Cu 2 O, and iron oxides, Fe 2 O 3 and/Fe 3 O 4 , on the AE 3 outer layer. The chemical composition of the corrosion products is related with the soil composition, a sandy neutral soil, rich in P, Mn, Si, K, Fe and organic matter (9%). The hydrogeological context plays also its role on the formation of the corrosion products.