Why does a pile of coins left alone for long periods of time get that “icky” dirty feeling and grime to them?

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Why does a pile of coins left alone for long periods of time get that “icky” dirty feeling and grime to them?

In: Chemistry

Fresh coins wouldn’t, i suspect.

I believe this is because they’re covered in oils from our skin (which is also what makes them smell of metal) that pick up dust and fluff from the air over time.

It’s called “corrosion”. Basically the metal on the coins react with the air and with the humidity of the air, creating ions. That layer of ions will protect the rest of the coin and that’s why the texture of the coins change.
For example, the Statue of Liberty is made out of copper, which has a dark brown colour, but the Statue of Liberty is kinda green. That is a layer of oxided copper, and it prevents the rest of the copper from vanishing due to corrosion.

People here are addressing the smell, which is indeed a chemical reaction with the skin, however I assume you mean they literally get dirty.

That’s not a quality of coins, it’s a cause from your medium of storage.