Abstract Seven coins, covered with black concretion coating, found in the Byzantine-period Ma'agan Mikhael B shipwreck, were examined in this study. Metallurgical methods comprising visual testing, XRF, multi-focal light microscopy, SEM-EDS analysis and Raman spectroscopy, were used to determine the corrosion products and microstructure of the coins. The analysis results show that the coins were made of copper-lead alloy with a heterogeneous microstructure of bright and dark metal areas. The external surfaces of the coins were mostly composed of oxides and corrosion product compounds rich in Cu, Pb and Sn, while the external dark concretion coating was rich in Si, S, Ca and C compounds. Gradual variation of the composition and structure of the oxides and concretion coating layers was observed. Highlights • Copper-lead coins covered with concretion were retrieved from a Byzantine shipwreck. • The coins are made of copper-lead alloy with heterogeneous microstructure. • Various oxides and corrosion products were observed on the coins' surface. • The concretion coating is rich with Si, S, Ca and C compounds. • A gradual variation of the concretion's composition and structure was observed. [ABSTRACT FROM AUTHOR]