Coin currency will degrade when left to the natural environment, forming mineral products as corrosion. The purpose of this study was to document the corrosion mineral products of coins and their relative extent in different environments. This information would be useful to the U.S. Mint and to forensic scientists, who may wish to know the type of environment corroded coins from a crime scene had been in. We choose to analyze dimes, nickels, and pennies, in three different environments. Nickels and dimes are clad in cupro-nickel, 75% Cu and 25% Ni. Pennies are made from mostly copper or copper-clad zinc, depending on their year of manufacture. The three environments chosen for this study included a salt water tidal flat (Emerald Isle Marsh), a highly oxygenated, fresh water stream (Bent Creek), and a brackish water coastal inlet (Anderson Dock). Main methods for analysis included scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) and powder X-ray diffractometry (XRD). SEM provided visual and textural analyses, EDS provided mineral identifications based on chemical analyses, and XRD provided mineral identification based on crystal structure. A total of seven minerals were identified. Coins exposed to salt water, at Emerald Isle Marsh and Anderson Dock, had more severe corrosion than coins in freshwater, at Bent Creek. At Emerald Isle March, old pennies formed bornite (Cu5FeS4), and new pennies formed atacamite (Cu2(OH)3Cl), connellite (Cu19Cl4(SO4)(OH)32×3H20), and smithsonite (ZnCO3). Anderson Dock had cuprite, chalcocite (Cu2S), and simonkolleite (Zn5(OH)8×H20) on young pennies, and atacamite on old pennies. Nickels at Emerald Isle and Anderson dock had cuprite (Cu2O) and atacamite (Cu2(OH)3Cl). Nickels at Emerald Isle also formed Chalcocite (Cu2S). At Bent Creek, only atacamite was tentatively identified on all coins. No nickel minerals were identified on any samples.
