How Does a Coin Become ‘Rusty’?

Coins become ‘rusty’ because they react with air and water. When a coin is exposed to oxygen, it starts changing color, like turning from silver to brown or green. This happens slowly over time, just like how your skin changes when you spend too much time in the sun.

What Causes It

Coins are usually made of copper or other metals that react with air and water. When they meet these elements, a chemical change takes place, making them look different.

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Examples

A penny left in a jar with water turns green after several weeks.
Your old nickel from the 1980s has brown spots because it rusted over time.
Coins on a kitchen counter turn green if they are near a window where they get wet from rain.

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Categories: Science · chemistry,oxidation,coin rusting,metal reactions