I found a 1954 nickel but it is half the thickness of a regular nickel. Has anyone heard or seen anything like that?
It appears the coin has been immersed in some kind of acid which has eaten away a good part of the coin.
That is not true. Many people think this because they think that the the image on a coin only exists on the surface. And that if the surface is eaten away that the image will no longer be visible. But because of the nature of metal, when a coin is struck the metal that forms the image is compressed, made more dense. And thus when the metal is eaten away by acid the metal forming the image is eaten away at a slower rate than the metal surrounding the image. Thus the image will visible until the very end when the coin is completely dissolved by the acid. You can test it and see it for yourself.