Found this 1990 nickel in a roll last year and kept it because it was intriguing. The rim looks like it was rolled and made it round and smooth and thicker. I hope the pics help explain it. It's diameter is slightly smaller than a regular one. Do you think someone was just messing around and somehow rolled it on its edge and smashed it?
Someone tediously tapped the edges of the coin was a spoon until they became more rounded and have a similar appearance to your coin.
