So I was going through my coins adding in ones that I haven't put into my coin holder. This nickel caught my eye, I'm sure it hasn't been the first time either. But looking more at it in realising it's a nickel minted on a penny planchet. Sadly in really thought condition. It's a 1972. I'll provide photos
I was wondering if it was gonna have missing edges or not. I didn't even notice. This nickel just doesn't look of zinc or whatever they use.
"Nickels" are struck from an alloy that's 75% copper, 25% nickel. When they get corroded due to environmental exposure, the nickel gets eaten away faster than the copper, and you can end up with a brown coin like yours. It may weigh noticeably less than a normal nickel, but not enough less to match the 3.1g weight of a copper cent planchet.
A true nickel struck on a cent planchet would be the same weight, size and thickness of a cent. Unfortunately your nickel has environmental exposure toning damage as mentioned before. Not a mint error of any kind.
Here are many toned nickel examples I have metal detected. They were buried for many years and exposed to the elements.
Someone found it on the ground and put it back into circulation. Just toned from the environment. Only worth five cents.
Just ED, or environmental damage, @darkrainnn. As @paddyman98 posted, lots of nickel will turn the color of copper after exposure to the elements. Keep looking.