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What is the greenish-blue sand like substance from a quarter, dime and penny in saltwater

Hello,

I'm in 6th grade and performing an experience to determine if US coins rust faster in saltwater or tap water. I quickly realized that this was a trick question because US coins do not contain iron so they do not rust, however they can corrode. Ten days into my experiment in which I placed a quarter, nickel and penny in saltwater, I noticed a greenish-blue substance, which looked liked sand, on the bottom of the containers holding the coins and the saltwater. I'm curious, which coin combines with saltwater to produce this greenish-blue substance and what is the greenish-blue substance/particals? My guess is the particles are part of the copper corrosion process.

Thanks,
Tommy

Tommy C.
Student - Spencerport, New York
2007

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Tommy,
Why not conduct a search of US coins on the internet to see exactly how each coin is made? Split up the coins and run separate experiments on each denomination. By doing this the teacher can't say "how do you know the greenish- blue salt didn't come from the nickel or dime?" You are on the right track with the penny though.

Mark Baker
Process Engineer - Syracuse, New York
2007